covert_shores

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List compiled from the excellent book The Silent Deep: The Royal Navy Submarine Service since 1945

BOREAS Class - page 131
1950s diesel-electric SSK. Smaller complement to PORPOISE Class.
1200 tons
'high quiet speed'
4 x TT in bow, 2 x TT in stern
Baseline version with twin screws, then single screw and HTP variants


1950s SSK with teardrop hull - forgot page #
In discussion after Mountbatten toured USS Albacore. Was to enter service in 1960s but abandoned when DREADNOUGHT (SSN 101) started. Instead OBERON Class was adopted as lowest risk/cost option for SSK


Hybrid SSN/SSBN - page 214
Based on VALIANT Class SSN but with 6 Polaris SLBMs - instead followed American strategy of keeping SSN and SSBN roles separate even though this delayed SSN production


'Harold Wilson Class' SSN - page 240
Contingency design in case the government (of Prime minister Harold Wilson) cancelled Polaris. rebuilding the RESOLUTION Class SSBN as a pure SSN. Similar to Valiant but 30ft longer

more to come



anyone know more or have plans?
 
The 'Silent Deep' is indeed an excellent book. I'm about half-way through it at the moment.

D.K.Brown & George Moore 'Rebuilding the Royal Navy' has:

1945 Programme
1,700 tons, twin screw HTP powerplant with 6,000shp per shaft, submerged max speed 21kts, planned to lay down 1947 to complete 1950. Cancelled in favour of two experimental subs, Explorer and Excalibur.

Boreas Class
The single-shaft design was quieter and 1kt faster. Plans for six twin-screw and nine single-screw subs. The single-shaft design would have no stern tubes. Four bow tubes and one countermeasures tube. Oddly, the original 1952 Staff Requirement called for a 4in Mk.XXIII to be mounted if required for non-ASW roles.
1,100tons (possibly the single-shaft version?)
10kts sub (8kts snorting), 11kts surfaced
Battery endurance 30 hours at 4kts
Some thought to fitting later vessels with re-cycle diesels.

1970s SSN Designs SSNOX, SSNOY, SSNOZ
Cheaper 'Improved Swiftsure' procured instead as Trafalgar Class.
SSNOZ I think had the sail right forward, I remember there was a post on these on the lost Warship Discussion Forum too.

There were several early proposals for the Upholders too, but I want to wait until I've read more about the latter designs in 'Silent Deep' before describing them here.
 
Sounds pretty compelling to me. Further, is it certain from those sources that the "O" in SSN-O* is actually a capital letter O, or could it be a numeral 0 (zero)?
 
I think the designation follows numerically from previous classes i.e Dreadnought was SSN01, Valiant SSN02 and class, Swiftsure SSN07 and class. As I see it, SSN0X, Y and Z would just be a hypothetical follow on.
 
More from 'The Silent Deep'

Upholder
Like Brown & Moore, mentions the various designs leading to the final Type 2400 design, but gives the designations.

A1: 62m long, 7.3m diameter 1,960 tons submerged
B1: 67m long, 7.6m diameter, 2,250 tons submerged
D1: 75m long, 7.6m diameter, 2,650 tons submerged

A1 was quickly discarded, the Naval Staff preferred B1 but Vickers preferred the increased size and range of D1 for export, but was too big for the operational requirements and too expensive to meet the cost-effectiveness versus the SSN.
So Director General Ships drew up a revised B1 with internal rearrangements and 2,400 tons submerged displacement, sufficient fuel for 24,000 miles and 28 days on station could be carried and the design could be stretched further.
Brown & Moore mentions Option-2 'B1' had the superior weapon fit with sub-Harpoon, but Hennessy & Jinks point out the Upholder had no anti-ship role so only carried torpedoes.

SSN0Y
As JFC Fuller pointed out, this was the Trafalgar design. SSN0X is not actually mentioned in the text for the Swiftsure class, but it would be SSN0X logically. The origins of SSN0Y was 1968 when Rolls-Royce began work on a new series of reactors, Core Z, for Trafalgar tested at Dounreay in 1973/74.

SSN0Z
First studies date from 1969 as an SSN for the 1980s. Outline Staff Target OST 7052 issued for SSNoZ in May 1978. At least five other studies for cheaper cost were also considered before work stopped in autumn 1980 when work began on the Trident SSBN.
It was to use the PWR2 reactor and be fitted with an integrated sonar system and a new combat system. The designs ranged from 6,500 to 7,300 tonnes and roughly cost 38% more than Trafalgar. It was deemed over-ambitious and expensive and was shelved.

However, it was felt a new design was needed, quality mattered more than quantity, the RN could only afford a maximum fleet of 20 SSNs and with retirements it was estimated the fleet would shrink to 18 by 1991 and 15 by 1999. A new SSN should be ordered by 1992, needing a Staff Target by 1985. Building more Trafalgars was ruled out as they had origins in 1950s technology.

Studies began again. First being 2,800-3,000 tonne designs, Nuclear Patrol Submarines, based on Type 2400 with a new low-powered reactor. They were cheaper, but inferior to Trafalgar's performance but designing a new powerplant was unfeasible in a short timeframe.
PWR2 was confirmed as the powerplant of choice, resulting in a minimum displacement of 5,000 tonnes. In late 1982 preliminary work began on a design based on Trafalgar but with a cost increase of 10%, rather than the 38% of SSN0Z, max displacement dived of 5,000 tonnes. The aim was to complete design work in 1985, order the first in 1992 and commission in 1998.

Batch II Trafalgar
Work on the 1982 Trafalgar +10% cost seems to have soon stopped. A Staff Target was issued in 1986, Full Feasibility Studies on the 'Follow On SSN' by VSEL were undertaken 1986-89 and the Staff Requirement not issued until August 1989. The first acceptance date was delayed to 2000. By 1990 several studies were underway, including improved and stretched Trafalgar designs as well as new designs. This crystallised as Trafalgar Batch II. Rather than using new equipment like SSN0Z, the Batch II would use the best of Trafalgar, Vanguard and Upholder technology. This work, after trials and tribulations with VSEL and BAE Systems (not least lost expertise following the end of the Vanguard programme) led to the Astute Class.
 
Couple of additional snippets on Upholder.

Later subs in the class were to have increased bunk space, rotating conversion machinery with static inverters, increased fuel capacity by using spaces outside the pressure hull, and more long-term, experimental fuel cells to reduce snorting time.

When placed up for disposal the other nations besides Canada the government tried to interest were; Chile, Greece, Pakistan, Portugal, Saudi Arabia, South Africa and Turkey.
 
Interesting article from 1982 from the Journal Of Naval Engineering here. References Swiftsure class as SSN0X.
Some good stuff all round on this site, though obviously biased to engineering subjects.

http://www.jneweb.com/EntityFiles/5/1499/JNEPaperFileName/v27b1p01a.pdf
 
covert_shores said:
How big was the difference between swiftsure and trafalgar really? Other than the reactor core, it seems pretty minor.

The change to pumpjet propulsors in Trafalgar hull 2 and later was a big deal.
 
Propulsor (or pumpjet) was already in service after trials on Churchill. S boats had Propulsor from Sovereign onwards, Trafalgar had a conventional prop. T class Propulsor is changed from post swirl to pre swirl design (rotor and stator reversed). Main differences between S and T are that T is two frames longer, internal layout forward is changed too, mainly in Control Room. New sonar 2020 replaced 2001. Aft there is a further reduction in hull openings (combined coolers for auxilliaries and reactor cooling instead of separate) and again some layout changes including two diesel generators instead of one. More machinery raft mounting for noise reduction too (T boat MUCH quieter than S). Having served on both, accomodation was worse on T, but British nuclear submarine design has made accomodation steadily worse since Dreadnought.
 
I should have remembered the Swiftsures had propulsors. Why did Trafalgar switch back? Trouble with the new propulsor design?
 
Thanks aircondoc, very insightful.

The differences are fascinating but probably less than what would be a sub-variant in other classes.

Seems the opposite is true compared to SDVs. With SDVs whole new classes are denoted by a 'mod1' suffix on their predecessors in order to trick the accountants. Whereas in British SSNs follow-on variants are subject to a whole new class. ;)
 
Hood said:
Couple of additional snippets on Upholder.

Later subs in the class were to have increased bunk space, rotating conversion machinery with static inverters, increased fuel capacity by using spaces outside the pressure hull, and more long-term, experimental fuel cells to reduce snorting time.

When placed up for disposal the other nations besides Canada the government tried to interest were; Chile, Greece, Pakistan, Portugal, Saudi Arabia, South Africa and Turkey.

I think you've forgotten Australia in that list...
 
Australia was not on the list quoted, the source Hennesy/ Jinks used was David Peer, 'Some History of the Upholder-Class Submarines', Canadian Naval Review, May 2012

From what I've read, Australia was never interested in the Upholders due to their short-range, instead holding a competition for a new design to meet their requirements, which became the Collins.
 
Hood said:
Australia was not on the list quoted, the source Hennesy/ Jinks used was David Peer, 'Some History of the Upholder-Class Submarines', Canadian Naval Review, May 2012

From what I've read, Australia was never interested in the Upholders due to their short-range, instead holding a competition for a new design to meet their requirements, which became the Collins.

The Upholder was pitched to Australia as a supposed gap filler to cover the combat system problems the Collins class was having during its first 10 years. The Upholder was assessed by the DoD and RAN and was found to be far worse than the Collins at the height of its troubles. The last two Collins recieved a major patch on the CMS and the entire class refitted with the USN's BYG-2.

The Upholder offer was great for Australian morale as it put the problems of the Collins class into light. Unfortunately none of this was adequately communicated to the government elites and the perception that Australians can't build boats remain so now we have to Frankenstein some more overseas marque to meet Australian requirements rather than build our own, far superior design. You would think that after making this same mistake three times in a row* we would learn?

*:
1. Protector AOE vs Durance AOR
2. DDL vs FFG
3. Evolved AWD vs F100
 
Its called the cultural cringe the perpetrators of which are our political, media, financial, small business, primary producers and resources sectors, the section of the economy and society that are largely non-technical in nature and cannot comprehend that people they look down on, engineers, designers, technical officers, trades and even production workers might actually be good at what they do. In fact if you look at it Australia has a tradition of exporting technical and scientific talent, people who are treated as incompetent rent seekers locally but excel on the global scene.

It all comes down to who is making the decisions, their backgrounds and life experiences; unfortunately the size of someone's pay check also determines their perceived worth and technical and scientific roles don't pay anywhere near as well as financial services etc. Sorry about the rant but it is a sore point, having worked R&D in Australia's automotive industry, then engineering and test in defence (subs, destroyers and PBs).

By the way the Upholders were an absolute mess, never a match for the Collins, especially after being laid up for so long before their sale to Canada. On ex UK TO on AWD piped up that Australia would be much better off had they bough Upholder, poor bloke made the comment within ear shot of some who had first hand experience with Collins and was put straight very quickly.

Wasn't there a W Class SSN using the reactor of the Vanguards planned for the 90s but cancelled as part of the "peace dividend"? I recall an ex UK colleague mentioning it at one point, he had cut his teeth on the Ts.
 
Volkodav said:
Wasn't there a W Class SSN using the reactor of the Vanguards planned for the 90s but cancelled as part of the "peace dividend"? I recall an ex UK colleague mentioning it at one point, he had cut his teeth on the Ts.

Indeed, the W-Class, also known as the SSN20 project.
 
The second Batch of Upholders: In 1985 it was reported that the UK had told the Australians that the UK would order the Type 2400A version (lengthened for Australia with a third diesel engine) if they ordered it for what became the Collins class. Ferranti Thomson was developing Sonar 2075 for the second batch of Upholders and they would apparently have been fitted with SMCS as well.

What is difficult to decipher is numbers. The Nott review took the fleet/patrol submarine force down to 28 boats which was to remain "generally constant" and the fact sheet that accompanied options for change stated that the RN had 27 attack submarines. The Nott review had been aiming for 17 SSNs by 1990 and that was achieved with the commissioning of HMS Talent in May that year, HMS Triumph's commissioning would have got the fleet to 18 in 1991 had it not been for Options for Change. Things get complicated because the second batch of Upholders would have been ordered around the same time as the W-Class SSNs. Jane's reported that five additional Upholders were planned and seven W-Class boats which gets to a total fleet (including Swiftsure's and younger) of 29 boats which to my mind makes one or both of those numbers unlikely. Ministers seem to have been very coy about giving numbers for the second Upholder batch too.

Vanguard Class Boat 5: Right at the beginning of the Trident programme (1979) consideration was given as to whether the trident force should be four or five boats (with obvious parallels to the Polaris programme in the 1960s. In July 1980 the then Defence Minister (and direct predecessor to John Nott) Francis Pym said the following to the House of Commons:

The agreement that we have reached is on the same lines as the 1962 Nassau agreement, under which we acquired Polaris. We shall design and build our own submarines and nuclear warheads here in the United Kingdom, and buy the Trident missile system, complete with its MIRV capability, from the United States. Once bought, it will be entirely in our ownership and operational control, but we shall commit the whole force to NATO in the same way as the Polaris force is committed today. The new force will enter service in the early 1990s and will comprise four or five boats. We need not decide about a fifth boat for another two or three years, and we are leaving the option open meanwhile.

The decision against a fifth boat seems to have been made sometime in early 1982 with John Nott making the following remarks in the house of Commons in March 1982:

Because of the extended length of the refits—seven years—four Trident submarines are equivalent to at least five Polaris submarines. We do not now need to contemplate five submarines. Four Trident D5s, with a much longer refit interval and the in-tube life of seven years, plus the missile, are equivalent to more than five Polaris submarines. We shall have three in the operational cycle for a large proportion of the time.

Purely hypothetical but I quite like HMS Vindictive as a name for this contemplated fifth boat.

Unbuilt Vanguard/Trident support infrastructure: This explains the giant hole visible next to Rosyth Dockyard that Babcock is attempting to turn into a container port. This was the RD57 proposal that was abandoned in favour of concentrating nuclear submarine refits and refuelling at Devonport after the end of the Cold War:

Of the available documents for the RD57 project, two dry docks, workshops, offices and support facilities on a site at the west end of the Base are mentioned. Under RD57 one dry dock was designed to measure 190 metres in length by thirty metres in width, and the other to be 150 metres in length by twenty-eight metres in width. The main dock cover was also designed to be an estimated fifty metres wide, forty metres high at the highest point and a maximum of 200 metres long. This structure would not only protect against weather but would support the overhead travelling cranes necessary to perform various tasks. Furthermore, the two dock covers were to be linked to support facilities located both between and at the west end of the docks. Initial plans dictated that the complex was to be enclosed by security fences, with road and rail accesses and carparks provided. This project was thought to require fifteen hectares for the development, five hectares of which was existing Ministry of Defence land. Support services to the complex under RD57 were also intended to involve substations, stand-by power generating facilities, a compressor house, plant rooms, a materials storage area, external plant areas and demineralised water facilities, with design and construction of the facility subject to a quality assurance programme addressing safety and reliability in all matters relating to nuclear safety.

Source: http://theses.gla.ac.uk/6551/1/2004JamisonPhd.pdf

Whats curious is that this was built to west of the existing dockyard. As built a large area of land was drained/cleared/reclaimed to the east of the yard to provide for future expansion, for some reason this appears not to have been used for the RD57 facility.

Edit: Examining the RD57 site on google earth it looks like the foundations of the two dry docks were built- there are two long concrete structures in the hole that match the lengths described above. Based on their location it would seem that the entrances to the dry-docks would be directly from the non-tidal basin which would explain the decision to build the facility to the west of the existing dockyard rather than the east.
 
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Does anybody in a slight chance have sketch drawings of the HMS Dreadnought SSN Preliminaries? I've been intrigued by the 4 shaft design described having one propeller in each quadrant!
 
http://www.telegraph.co.uk/business/2017/08/27/manta-ray-submarines-flying-fish-torpedoes-navy-future-might/
 
More information here:
http://www.uknest.org/naval-programmes/concept-fleet/nautilus/

Two of my colleagues were involved in the workshop; the terms of reference were basically to come up with as many potential applications for new technologies in submarine warfare as they could, regardless of technical feasibility.
 
A document from 1981 confirms that the force goal of 20 SSNs was changed in 1980 by the inclusion of the Trident boats into the Long Term Costings (LTC) for the first time. This introduced a break in the SSN build programme after SSN19 (HMS Triumph) which put downward pressure on the maximum number of SSNs that could be kept in service so the fleet would peak at 18 units in 1991 then decline to 15 by the mid-1990s where it would remain well into the 2000s.

My own view, though as yet I have no evidence, is that the number may have crept back up to 18 (or more); that would explain the decline in planned SSK numbers versus the overall submarine force goal. This probably being achieved by life extensions to existing boats.

This has also solved another little mystery. All the files labelled SSNOZ date to the 1970s despite the fact the programme appears much later. It transpires that the reason for this was that SSNOZ was originally planned to follow SSN19 in production but this couldn't happen because of the Trident programme so the designation and project were put on the back burner. Thus SSNOZ actually has two lives- one in the 1970s and then another in the late 1980s.
 
Abraham Gubler said:
Hood said:
Australia was not on the list quoted, the source Hennesy/ Jinks used was David Peer, 'Some History of the Upholder-Class Submarines', Canadian Naval Review, May 2012

From what I've read, Australia was never interested in the Upholders due to their short-range, instead holding a competition for a new design to meet their requirements, which became the Collins.

The Upholder was pitched to Australia as a supposed gap filler to cover the combat system problems the Collins class was having during its first 10 years. The Upholder was assessed by the DoD and RAN and was found to be far worse than the Collins at the height of its troubles. The last two Collins recieved a major patch on the CMS and the entire class refitted with the USN's BYG-2.

The Upholder offer was great for Australian morale as it put the problems of the Collins class into light. Unfortunately none of this was adequately communicated to the government elites and the perception that Australians can't build boats remain so now we have to Frankenstein some more overseas marque to meet Australian requirements rather than build our own, far superior design. You would think that after making this same mistake three times in a row* we would learn?

*:
1. Protector AOE vs Durance AOR
2. DDL vs FFG
3. Evolved AWD vs F100
sorry for the late reply. Was the initial combat system, which was so troublesome, Swedish?

Reason I ask is because i hear impressive things re the Swedish systems from people with first hand experience, but not Australian. Record for most wire guided torpedoes 'in flight' is Swedish?
 
A list of submarine projects from Friedman’s British Submarines in Two World Wars, many of which I suspect haven’t been covered elsewhere before, even D. K. Brown’s series. This list only gives brief details as I wouldn’t want to spoil anyone’s enjoyment of the book.
[Dimensions are overall length x diameter; (surf) = surfaced; (sub) = submerged]

C2
Offered by DNC June 1905 as an alternative choice to the D-class. A C-class with extra tankage and increased freeboard, 19ft diameter hull. Rejected as the ‘D’ was superior due to its saddle tanks with a better shaped hull for diving and steering when dived.

Vickers Alternatives to the D-class
In April and May 1906 Vickers proposed three alternatives to the D-class that the RN wanted;
Design E1 – a larger B-class with improved hullform, 152.5ft x 14.75ft, 437 tons (sub)
Design E2 – a larger B-class design with improved hullform, 155ft x 15.3ft, 482 tons (sub)
Design E3 – as E2 but 15ft 9in diameter for improved stability, 495 tons (sub)
All were rejected. Vickers resubmitted E3 in August 1906 but was rejected again.

C-class Derivatives
In 1908 the DNC effectively re-visited Vickers’ suggestions from 1905 in an attempt to find a cheaper design than building five more D-class subs; a C-class with a 600hp Vickers diesel or an enlarged ‘C’ with twin propellers and two 600hp diesels. These were rejected but another modified ‘C’ with D-class features was offered, again with twin propellers, 2x 700hp diesels, 7ft 3in longer hull, 13.25kts (surf), 500hp electric motors. This redesign was rejected as too expensive.

FIAT Design
Offered 1909.
157.5 x 17.4ft, 558 tons (sub), 4x torpedo tubes (8x torpedoes), 2x 500hp petrol engines, 14kts (surf), 9.5kts (sub), 80nm at 4kt (sub)

Scott Laurenti Designs
Offered November 1909, licenced Laurenti design.
A: 148 x 13.8ft, 380 tons (sub), 400hp diesel, 12.5kts (surf), 8kts (sub), 75nm at 4kt (sub), 2x torpedo tubes (2x torpedoes)
B: 148 x 13.8ft, 380 tons (sub), 300hp diesel, 10.5kts (surf), 7.5kts (sub), 80nm at 4kt (sub), 2x torpedo tubes (2x torpedoes)

Thornycroft Lake Designs
Offered 1909, licenced American Lake design. Thornycroft had offered a submarine design in 1903 but Friedman gives no details.
A: 161 x 13ft, 525 tons (sub), 2x 600hp diesels, 14kts (surf), 9.5kts (sub), 96nm at 4kt (sub), 6x torpedo tubes (2x rotating & 4x fixed) (6x torpedoes)
A: 161 x 13ft, 475 tons (sub), 2x 600hp diesels, 14kts (surf), 9.5kts (sub), 96nm at 4kt (sub), 4x torpedo tubes (8x torpedoes)

E-class Alternatives
The designs for what became the E-class included a number of proposals, among which were an ‘Italian’ design, presumably a Laurenti design, and Vickers offered the ‘modified D’ with Belgian Carels or Vickers diesels

1910-11 Programme 20-knot Submarine/ 1911-12/ 1912-13 Programme Big Submarine
One submarine planned. Given the size and expense of the submarine the submarine was postponed for the 1911-12 and then the 1912-13 Programmes.
The DNC sketched a design: 870 tons, 210ft long, 2x 2,400hp Carels diesels, 20kts (surf), 4,000nm at 10kts (or 13?), 10.25kt (sub), 7x torpedo tubes (2x bow, 1x stern & 4x broadside)

DNC refined this design as the Carels engine failed to materialise and three smaller diesels were required: 230ft 10in x 23ft 6.5in, 1,160 tons (sub) (later increased to 1,203 tons), 3x Vickers diesels, 19kts (surf), 1,660nm at 16.5kts, 1,350hp motors for 11kt (sub), 7x torpedo tubes (2x bow, 1x stern & 4x broadside – 14x torpedoes), 2x1 12pdr QF

This design was further refined and Haslar tank models included; TG (enlarged E-class), TJ (partly circular-pressure hull), TK (double-bottomed). Beam was now 23ft (22ft 7in for TG), displacements 1,158 tons, 1,034 tons, 1,301ton (sub). With only 3,200hp speed fell to 17.7-17.2kts, range fell to 2,640nm, 3,000nm, 2,540nm respectively at 11kts.

Another E-class development was also offered; 240 x 24ft 5in, 10kts (sub), 8x torpedo tubes (2x bow, 2x stern & 4x broadside – 20x torpedoes), 1x 12pdr QF

Other proposals were a ‘French’ Laubeuf design which was based on a design Laubeuf had offered to Chile and an ‘Italian’ Laurenti design (possibly Haslar model TK).

G-class Alternative
When the G-class was formulated, Vickers tendered a design alongside the DNC design; 185 x 22ft 6in, 1,090 tons (sub), 1,600hp total using Vickers diesels, 15kts (surf), 2,600nm at 10kts, 840hp motors for 9kts for 1hr (sub), 70nm at 5kts, 1x 21in bow torpedo tube & 4x 18in broadside tubes, 1x 12pdr QF

FIAT Design 140
Offered in competition with Scotts Laurenti design which became Swordfish; 240 x 22ft 8in, 1,570 tons (sub), diesel engines for 18kts (surf), 3,500nm at 10kts, 3,250hp motors for 10kts (sub), 1x 21in bow torpedo tubes, 2x 18in stern & 4x broadside tubes
The Design 140 was modified as the Design 140bis; 224 x 23ft 3in, 1,230 tons (sub), 18.5kts (surf), 3,600nm at 10kts, 3,250hp motors for 10kts (sub) 2x 21in bow torpedo tubes & 4x 18in broadside tubes
The Design 140bis was further modified with a steam turbine powerplant; 231ft 1in x 23ft, 1,024 tons (sub), 18kts (surf), 3,000nm at 8.5kts, 10kts (sub), 2x 21in bow torpedo tubes & 4x 18in broadside tubes

K-class Re-engine Proposals
Brief post-war ideas to replace the steam powerplant in the K’s:
3x 3,000hp diesels at a cost of 250 tons and 1kt of speed, doubtful if would fit
3x 3,000hp diesels driving two shafts and a 2,060kW generator at a cost of 50 tons and speed would be 22.6kts

1915 Submarine Design Committee Types
In September 1915 the Submarine Design Committee considered six types; coastal, patrol, fleet, cruiser, minelayer, monitor. Only the cruiser and monitor submarines did not exist at that time.

The committee asked DNC d’Eyncourt to draw up a C Class replacement, requirements were; 500 tons, 13-14kt (surf), single-hull construction and a 12pdr gun. DNC used a hullform similar the US H-class. Details no longer survive.

The patrol type was split into slow (E & G-classes) and fast (J-class) types. d’Eyncourt sketched an improved ‘G’ with better habitability, no stern torpedo tube and a longer hull. This was later replaced by the ‘elongated E’ which became the L-class.
The new fast type d’Eyncourt sketched was a J-class modified for a steam powerplant with any space saved going to improve habitability and weight savings into fuel bunkerage.

The cruiser submarine was based on the K-class with a reduced 5,500hp steam powerplant but with increased electric motor power and 2x1 6in guns, 4x bow & 4x broadside torpedo tubes. Range would be 10,000nm at 10kts.

The monitor was based on the K-class; 320 x 40ft, 4,000 tons (sub), 5,000hp steam on the two outer shafts & 1x 1,000hp diesel on the centre shaft, 19-20kt (surf), 2x 7.5in or 1x 12in forward & 1x 4in or 6in aft, 4x 21in bow torpedo tubes. The committee favoured the 7.5in gun but asked DNC for further designs with 1x 12in forward and 2x1 12in (fore and aft). These designs resulted in the M-class.

In 1916 the d’Eyncourt proposed a 30kts cruiser submarine, again details are lost to history.

L-class Preliminaries
Originally the torpedo armament was 4x 18in bow tubes & 2x broadside tubes but by November 1916 the broadside tubes were dropped and the bow battery upgraded to 21in.
The gun armament was originally 2x1 3in 12cwt but later replaced by 1x 3in HA on a retractable mounting.

The ‘L cruiser’ had 2x1 5.5in guns or 1x 5.5in & 1x 3in HA, this was reduced to the 2x1 4in actually fitted to the L50-class. The 4x 21in bow tubes were later upgraded to 6x tubes for the L50-class. 234ft 4.5in x 23ft 7in, 1,122 tons (sub), 3,200hp diesels, 18.25kt (surf).

Beatty’s Cruiser Submarine
In response to a letter from Admiral Beatty on 22 January 1918, DNC drew up a sketch design for a cruiser submarine capable of 32kts and armed with 3x1 6in and 1x 3in HA and 8x 21in bow torpedo tubes. The sketch is now lost but this was the starting point of the subsequent post-war X1.

X1 Preliminaries
X1 began as a 2,680 tons (surf) design with 3x1 4in guns with a 9ft rangefinder and a DCT. DGD wanted 6in guns but eventually settled on an experimental twin 5in mount, DNC favoured a twin 4.7in. As completed she received 2x2 5.2in mounts.

Aircraft-Carrying Submarines
When studying the conversion of M2 with a hangar and catapult, DNC also looked at converting a K-class with a cylindrical hangar, the aircraft requiring assembly on deck before the stern was submerged to float the seaplane off. DNC also studied putting the same hangar onto the new O-class patrol submarines. There is also evidence that the R-class were studied with a hangar added for one seaplane.

Vickers Fleet Submarine
In June 1925 Vickers offered a diesel-powered fleet submarine to the Admiralty guaranteed to make 23kts for 1,600nm using four 3,000hp diesel engines mounted in two tandem pairs;
351 x 28ft, 2,300 tons (surf), 23.5kts (surf), 9kts (sub) [DNC felt this was optimistic], 6x 21in bow torpedo tubes & 2x 21in external bow tubes, 2x1 4.7in guns and 1x 40mm pom-pom, 300ft diving depth.

Thames-class Preliminaries
In May 1928 DNC offered a series of sketch designs. All were under 1,800 tons, 200ft diving depth, 2,460hp electric motors, 12,000nm at 12kts and shared the same armament of 6x 21in bow tubes and 1x 4in HA gun. None offered more than 22kts (surf):
Design A – 2x 3,000hp Cygnet diesel (EinC project)
Design B – 2x 10-cylinder diesels based on engine used in X1
Design B1 – 2x 10-cylinder diesels based on engine used in X1
Design C – 2x 3,000hp Cygnet diesel (E-in-C project)
Design D – 4x 2,200hp diesels as used in Odin-class in two tandem pairs, layout rejected by EinC
Design G - 3x 2,200hp diesels as used in Odin-class driving triple shafts, could achieve 21kts
Design H – 2x 4,300hp AEL diesels, rejected due to long engine unacceptably increasing length
Design J – 3x 10-cylinder development of 2,200hp diesels as used in Odin-class driving triple shafts

J was considered the minimum acceptable design but G was preferred but the estimated £460,000 cost was high. G went forward for further development, a two-shaft version (G.2) being drawn up with supercharged diesels. G.2 was then further refined into the Thames Class.

Minelaying Submarines
In 1923 the Superintendent of Mining drew up several schemes for internal minelayers (mines and launch tube inside the submarine pressure hull):
Type A – 2x vertical tubes launching 3x mines each at a time
Type B – 2x horizontal tubes launching 3x mines at a time
Type C – 2x vertical tubes launching 6x mines each at a time
Type D – 2x horizontal tubes launching 6x mines at a time
Type E – 4x vertical tubes launching 5x mines each at a time
Type F – 4x horizontal tubes launching 5x mines at a time
Type G – 1x vertical tube with 40x mines (how this fitted is unknown!!)
Type H – 1x horizontal tube with 40x mines
Type J – 2x tubes with 20x mines each
Type K – 2x vertical tubes launching 5x mines each at a time
Type L - ?
Type N – two horizontal tubes amidships launching 5x mines at a time with three mine stowage rails above

1924 DNC made the first sketch design but it seems no details are known.
Progress was slow, largely waiting for the conversion of M3 and the results of her trials. This resulted in 1929 DNC drawing up three designs:
Design A – a variant of the Rainbow-classs with external stowage for 40x mines requiring the conning tower, bridge and gun to be moved 42ft forwards. Stern torpedo tubes removed, power loading for bow tubes removed, 300ft diving depth, 1,505 tons.
Design B – as A but with another 40x mines in a stowage box ahead to balance the design so the conning tower could be moved back to the centre, 1,750 tons. Rejected due to large silhouette and displacement was too large for Treaty allowance.

Later DNC cut the surface speed of Design A from 17kts to 15kts with a streamlined watertight box over the bows for balance to enable the conning tower to be moved backwards but both A and B were rejected. DNC submitting two new sketch designs in September 1930:
Design C –again a modified Rainbow-class with 50x external mines, 1,490 tons.
Design D – an internal minelayer with 40x mines, used engines, batteries and motors from the S-class, 1,500 tons
Design E – a variant of D with reduced batteries, reducing speed and underwater range (11.5kts surf & 8kts sub).
The internal minelayer concept was abandoned as a reasonable mine load could not be carried on 1,500tons (40x mines was the minimum acceptable) and Design C was refined into the Grampus.

S-class Preliminaries
DNC began work on the S class for the 1929-30 Programme in 1928. He drew up three designs;
Design S1 – 177ft 6in long, 690 tons (surf), 800 tons (sub), 1,450hp for 14kts (surf), 3,250nm at 8kts, 840hp motors for 9kts (sub), 50nm at 4kts (sub), 4x 21in bow tubes (8x torpedoes), 1x 3in HA, 300ft diving depth
Design S2 – 186ft long, 800 tons (surf), 920 tons (sub), 1,650hp for 14kts (surf), 3,250nm at 9kts, 1,000hp motors for 9kts (sub), 75nm at 4kts (sub), 6x 21in bow tubes (12x torpedoes), 1x 3in HA, 300ft diving depth
Design S3 – 190ft long, 722 tons (surf), 835 tons (sub), 1,550hp for 14kts (surf), 3,250nm at 9kts, 1,305hp motors for 10kts (sub), 90nm at 3kts (sub), 6x 21in bow tubes (12x torpedoes), 1x 3in HA, 300ft diving depth

S1 was the preferred design and but DNC thought he could fit 6x bow tubes and S3 was the result which was then selected as the S Class.

1932 Geneva Small Submarines
As the Geneva talks got underway, the DNC was asked to sketch up a minimum submarine suitable for reconnaissance operations from Hong Kong with 5,000nm endurance. Even reducing the torpedo calibre to 18in was considered if newer models could be equally lethal. DNC drew up a design offered in two variant with one being fitted with two airlocks, which were becoming the newly desired feature for life-saving in the event of accidents when submerged with Davis escape gear.
Without airlocks: 209 x 26ft, 870 tons (surf), 1,100 tons (sub), 5,000hp for 12kts (surf), 1,300hp motors for 9.5kts (sub), 6x 21in bow tubes (12x torpedoes), 1x 3in HA, 300ft diving depth
With airlocks: 213 x 26ft, 900 tons (surf), 1,130 tons (sub), 5,000hp for 12kts (surf), 1,300hp motors for 9.5kts (sub), 6x 21in bow tubes (12x torpedoes), 1x 3in HA, 300ft diving depth

These were not considered ‘minimum’ enough but DNC also drew up a 250 ton (standard) design e based on the R-class; 126 x 13ft, 278 tons (surf), 328 tons (sub), 180hp diesel for 8.5kts (surf), 2,400nm at 8.5kts, 650hp motor for 12kts (sub), 12hrs at 12kts (sub), 4x 18in bow tubes (5x torpedoes), 300ft diving depth

This was followed by a more conventional design which was compared to the old C and H-classes:
240hp diesel for 10kts (surf), 3,450nm at 8kts, 4x 21in bow tubes (8x torpedoes), 1x 3in HA.
DNC estimated a minimum submarine for 6x 21in bow tubes would be 450 tons (surf) and 600 tons (sub) which would allow 11kts (surf), 3,000nm at 8kts, 9kts (sub), 44nm at 2kts (sub). Displacement could be cut to 435 tons with only 4x bow tubes.

In May 1932 DNC was then asked to design a 600 ton design, the result being a scaled down S-class; 192ft 6in x 24ft 4in, 685 tons (surf), 870 tons (sub), 1,050hp for 12kts (surf), 3,000nm at 8kts, 8kts (sub), 30nm at 2kts (sub), 6x 21in bow tubes (10x torpedoes), 1x 3in HA. Adding an airlock and battery cooling increased the length to 210ft and displacement to 900 tons (surf) and 1,130 tons (sub) and in compensation power and speed was cut to 1,350hp for 12kts.

DNC then sketched a 1,200 ton submarine, closer to the types that would soon be built as rearmament got underway; 255ft long, 1,400 tons (surf), 1,635 tons (sub), 3,300hp for 12kts (surf). The Geneva talks collapsed and the need to think about artificial arms limitations on displacement disappeared as the Treaty system slowly unravelled.

T-class Preliminaries
In 1934 work began on what became the T-class, its origin being a scaled up S-class for the Far East, being a replacement for the earlier fleet and submarines which were now considered too large and unwieldy and ill-suited to newer tactics.
Design A –260 x 22ft, 1,260 tons (surf), 1,540 tons (sub), 2,500hp for 14.8kts (surf), 1,300hp motors for 9kts (sub), used a Grampus midship section with internal fuel stowage in a keel ‘keyhole’ shape, this added weight, the battery needed 336-cells to achieve 9kts (sub)
Design B – 250 x 22ft, 1,195 tons (surf), 1,455 tons (sub), 2,500hp for 15kts (surf), 1,300hp motors for 9kts (sub), had a two-battery 224-cell layout to guarantee 55 hours at 1.5kts (sub)
Design C – 250ft long, 1,000 tons (standard), used battery layout of A with airless injection diesels, 14.5kts (surf), 8,600nm at 8kts

A Staff Requirement was written based on A and B but the Admiralty wanted more range which required further compromises in displacement and size. Further calculations were made for several alternatives; 1,059 tons with 2,500hp, 1,090 tons with 2,000hp and 1,108 tons with 2,400hp. On 9 May DNC calculated a 275ft long design with 125 tons of fuel (a 10 ton reduction). Before that, on 23 April 1935, DNC submitted Design D, which was 13ft shorter than Design C with a lower bridge and a 4in gun.

DNC then sketched up another design; 260ft long, 1,250 tons (surf), 14.5kts (surf), 3,000nm at 11kts, 6x 21in bow tubes and 2x external tubes. 4x external tubes were wanted however, pushing the design to 276ft 6in long, 2,500hp for 15.5kts (surf), 4,500nm at 11kts. There was much discussion of where the put the oil tanks, DNC preferring external tanks but their location took some refining to avoid loss of speed but this design was eventually accepted at 1,300 tons and 277ft long.

The 1939 Patrol and Minelaying Submarine
In December 1938 the planned 1939 minelayer (2 subs planned) was a modified Cachalot with a circular pressure hull and the high-capacity batteries as fitted to the T-class. Surface displacement increased to 1,755 tons, length to 273ft (between perpendiculars) and the range increased to 11,000nm.

The 1939 Programme also included two S-class and further improvements were sought. Almost as soon as the 1939 minelayer had been drawn up the First Sea Lord began looking at a smaller minelayer more suited to use in the North Sea and drawing on Vicker’s experience in designing the Kalev for Estonia.
DNC sketched a modified S-class; 725 tons (standard), 14kts (surf), 3,500nm at 10kts, 9.5kts (sub), 6x 21in bow torpedo tubes (12x torpedoes), 24x mines in 6 in open wells in the saddle tanks, 1x 3in HA. The external torpedo tubes were removed.
This was further refined, but without escape chambers to avoid congesting the hull; 218ft long, 815 tons (surf), 1,025 tons (sub) and the mine capacity reduced to 8-12x mines in 3 open wells. Including the escape chambers increased the length to 221ft 6in and displacement to 820 tons (surf), 1,030 tons (sub). Tenders were issued but work stopped due the 1939 war crisis, but the work would influence the 1940 S-class.

U-class Preliminaries
In March 1934 work began to replace the remaining H-class submarines being used for ASW training.
DNC drew up a sketch design on 19 April; 166ft 6in long, 420 tons (surf), 460 tons (sub), 525hp for 11.25kts (surf), 2,000nm at 10kts, 450hp motor for 9kts (sub), 4x 21in bow tubes (6x torpedoes), 2x Lewis MGs, 150ft diving depth.
As ever, the requirements began to grow; a 10-day patrol (equal to 3,160nm at 9kts), 6 bow tubes, battery recharging in 6 hours and even more difficult to achieve, a speed of 12kts (sub). Single and twin shaft layouts were studied. DNC began on a new design; 450 tons, 10kt (surf), 1,650hp motors for 12.5kts (sub). The first attempted hullform was rejected and the requirements were gradually relaxed, battery recharging in 6 hr 45 mins, 10kt submerged speed, two torpedo tubes were now external, pressure hull diameter increasing to 14ft 9in and submerged displacement grew to 615 tons.
Further refinements included commercial Paxman diesels and diesel-electric propulsion, 4x reload torpedoes (total 10) and endurance of 4,500nm at 8kts.

1941 S-class Replacement Designs
In late June 1941, Vice Admiral Submarines asked for a faster submarine capable of 17kts using existing engines;
Design A –179ft 6in x 21ft, 540 tons (surf), used the Paxman engines from the U Class boosted to 800hp for 12kts (surf), 4,500nm at 10kts, 825hp motors for 9kts (sub), 4x 21in bow tubes, no deck gun
Design B - ?
Design C – a modified 1940 S-class with a simplified structure, smaller diameter pressure hull and the AEL engines with solid fuel injection as trialled in HMS Sunfish, 220 x 21ft, 795 tons (surf), 915 tons (sub), 1,900hp for 15.5kt (surf), 6,000nm at 10kts, 1,300hp motors for 9.8kts (sub), 4x internal and 2x external 21in bow tubes and 1x external stern tube, 1x 3in HA
Design D – as C but with the Sulzer engines used in some T Class, 223 x 23ft 8.5in, 885 tons (surf), 1,060 tons (sub), 2,500hp for 16.75kt (surf), 6,000nm at 10kts, 1,300hp motors for 9.3kts (sub), 4x internal and 2x external 21in bow tubes and 2x external stern tubes, 1x 3in HA
There was little advantage over the S-class so production of the latter continued but with an external stern tube added.

1941 Minelayer
Two minelaying submarines were planned in 1941, being based on the Cachalot; 298ft long, 1,737 tons (surf), 2,085 tons (sub), two 8-cylinder versions of the T Class engine giving 3,300hp for 15.75kts (surf), 11,00nm at 8kts, 1,630hp motors for 8.75kts (sub), 6x 21in bow tubes (12x torpedoes), 50x mines.
The Legend was approved in April 1941 but the submarines were never ordered.

1941 Anti-Invasion Submarines
A series of small anti-invasion submarines were studied in June 1941 with simplified construction and operation to allow construction within eight months.
Design A – 160 x 21ft 1in, 462 tons (surf), 540 tons (sub), developed Vickers diesels as fitted to Estonian Kalev giving 500hp for 14kts (surf), 5,360nm at 8kts, 395hp motors for 8.75kts, 2x 21in bow tubes (stacked on centreline) (4x – later 6x – torpedoes)
Design B – 152ft 5in long, 434 tons (surf), 503 tons (sub), 4,450nm at 8kts, 2x 21in bow tubes
Design C – 160ft long, 489 tons (surf), 4,800nm at 8kts, 4x 21in bow tubes (6x – torpedoes)

1942 Minelayer/Replenishment Submarine
In February 1942, Vice Admiral Submarines felt that a replenishment submarine would be ideal to extend the range of existing patrol submarines, particularly the S-class. He asked DNC to merge this with the 1941 Minelayer. It would be around the size of the T-class carrying 120 tons of avgas in external tanks, 36x torpedoes in containers in the casing while being primarily designed to lay mines. Speed would be 18.5kts (surf). Another planned load was 600 tons of fuel plus torpedoes and mines. Friedman postulates that inclusion of avgas and torpedoes probably reflected the Malta resupply mission which became vital during 1942.

Due to staff shortages, Vickers was asked to draw up the preliminary design and it was sought to build the type in the USA due to shortage of slips in Britain. Vickers submitted the design in March 1943; 289ft 2in long (waterline), 2,494 tons (surf), 2,914 tons (sub), 430 tons of oil, 130 tons of stores, 24x torpedoes and 150x rounds of gun ammo.

U-class Projects
1942-43 project to fit a snorkel as an experimental testbed, no details known.
In 1944 work began on snorkel conversions with lead subs for each class for testing. Vickers was assigned to design the system for the T and U-classes. HMS Una was selected but no conversion was undertaken. The planned snorkel would only have folded above the periscope shears, the portion below being fixed vertically.

In 1944 attention also turned to a Fast Target on which to practice ASW techniques on the planned ‘Elektro’ U-boats. DNC initially focused on converting a U-class sub; fitting the 3,160hp motors from cancelled T Class subs replacing the existing engines and motors and a third bank of batteries replacing the torpedo stowage, the torpedo tube compartment becoming a mess space for the crew. Planned speed was 12kts (sub). External streamlining would be applied. Conversion would take too long however and the plan was dropped in favour of the S-class.

1944-45 Programme
The Admiralty planned one experimental and three ‘Improved A-class’ subs.

The ‘Improved A-class’ would have a telescopic snorkel, variable-pitch propellers, larger control room for an AIO, revised gun armament of 1x 4in & 1x2 20mm ahead of conning tower with 1x 6pdr aft. Streamlining was planned but the increase in speed was small. Around May 1945 it was decided that submersibles were no longer wanted, only true submarines with high-speed using snorts, HTP or closed-cycle diesels.

In February 1945 work began on the experimental susbmarine with an intermediate design hull and with a required speed of 20kts submerged which would need 8,000hp.
Design A – 266ft 9in x 23ft, 1,500 tons (sub), 560 batteries in five sections powering two motors providing 5,750hp for 18kts, endurance being 20 minutes at top speed, 2x 1,000hp Muscovic diesel generators were needed for recharging as standard diesels were not powerful enough alone, no armament and only one periscope.
This was further revised with six A-class batteries (131-cells each) without any diesel propulsion (recharging from a depot ship), 2x bow tubes &1x stern tube added to allow high-speed firing trials.
By late October 1945 four designs were being studied with different pressure hulls for diving depths down to 700ft and high speed; 18ft diameter circular, 19ft circular, 24ft circular, 17 x 23ft pear shaped;
Design C – 231ft 9in x 19ft dia pressure hull, 1,480 tons (sub), same powerplant as Design A, 14.5kts (surf)
Design D – 229ft 9in long, 1,430 tons (sub), 6x batteries, 6,900hp for 19kts (sub) for 20 mins
Design 1 – 165ft long, 24ft dia pressure hull, 1,240 tons (surf), 1,320 tons (sub), 6x A-class batteries (131-cells each) providing 8,000hp for 18+kts (sub), 2x bow tubes (6x torpedoes with reduced batteries), 500ft diving depth
Design 1A – 165ft long, 24ft dia pressure hull, 1,200 tons (surf), 1,280 tons (sub), 6x A-class batteries (131-cells each) providing 8,000hp for 18+kts (sub), 2x bow tubes (6x torpedoes with reduced batteries), 500ft diving depth
Design 2 – 22ft long, 19ft dia pressure hull, 1,285 tons (surf), 1,340 tons (sub), 6x A-class batteries (131-cells each) providing 8,000hp for 18+kts (sub), 2x bow tubes (6x torpedoes with reduced batteries), 600ft diving depth

These designs were compared against HMS Seraph’s conversion and an ‘improved Seraph’ DNC was also studying with a 0.625in thick all-welded pressure hull, two bow tubes (6x torpedoes), 2x 192-cell high capacity batteries from T-class, 4x S-class batteries driving 3,200hp motors for 15.5kts, 350ft diving depth. Another study was to fit a three S-class batteries for 2,400hp or 4x S-class batteries with T-class motors for 17kts.
These were all abandoned in favour of the HTP submarine (although some argued it was quicker to get an intermediate electro sub in service), and the ‘improved Seraph’ led to the later ‘super Seraph’ conversion of HMS Scotsman.

In July 1945 the ‘improved A-class’ was replaced by three new advanced submarines.
DNC looked at two projects; a Future Submarine with 24ft diameter pressure hull and 20kts submerged and a B-class with of A-class size with a 19ft diameter pressure hull. Armament was to be 6x bow tubes and if possible internal stern tubes.
In late October two preliminary B-class designs were drawn up;
BI – 2x 112-cell batteries (S-class size battery) and space for a Walter turbine
BII – 2x 112-cell batteries (A-class size battery) and space for a Walter turbine
Soon the Walter turbine was the preferred choice, twin 6,250shp turbines being favoured and later twin 7,500shp turbines. Problems were that 20kts was unlikely to be exceeded and endurance while snorting was shorter than surfaced endurance.
B1 – 1,770 tons, 2x 1,250hp diesels & 2x 7,500shp HTP turbines, 147 tons oil fuel for 8,000nm at 10kts (surf) or 5,500nm snorting, 6hrs endurance on HTP at 21kts (sub)
B4 – Friedman provides a drawing but no details, has 6x bow & 2x stern tubes.

Midget Submarines
In June 1940 Vickers proposed a minisub; 58ft 9 in x 7 ft 0.5in, 43.6 tons (surf), 88hp diesel for 6kts (sub), 1x 24.5in torpedo

Commander C. H. Varey (Ret.) original X-class design was; 30 tons (surf), 43ft 6in x 8ft

Varey also proposed a variant of the X-class with a conning tower; 60x 8ft, 46.4 tons (surf), 2x 42hp Gardner or 1x 85hp & 1x 20hp Gardner, 4,600nm at 7kts, armament choices of; 8x 150lb charges & 2x torpedoes in tubes or dropping gear & 2x 0.75 ton depth charges, 8x 150lb charges & 2x Chariots & 2x 0.75 ton depth charges or 8x 150lb charges 4x 1 ton depth charges
 
Fantastic post! Fairly sure only a minority of these get a mention in DKB's books.
 
Abraham Gubler said:
Hood said:
Australia was not on the list quoted, the source Hennesy/ Jinks used was David Peer, 'Some History of the Upholder-Class Submarines', Canadian Naval Review, May 2012

From what I've read, Australia was never interested in the Upholders due to their short-range, instead holding a competition for a new design to meet their requirements, which became the Collins.

The Upholder was pitched to Australia as a supposed gap filler to cover the combat system problems the Collins class was having during its first 10 years. The Upholder was assessed by the DoD and RAN and was found to be far worse than the Collins at the height of its troubles. The last two Collins recieved a major patch on the CMS and the entire class refitted with the USN's BYG-2.

The Upholder offer was great for Australian morale as it put the problems of the Collins class into light. Unfortunately none of this was adequately communicated to the government elites and the perception that Australians can't build boats remain so now we have to Frankenstein some more overseas marque to meet Australian requirements rather than build our own, far superior design. You would think that after making this same mistake three times in a row* we would learn?

*:
1. Protector AOE vs Durance AOR
2. DDL vs FFG
3. Evolved AWD vs F100
sorry for the late reply. Was the initial combat system, which was so troublesome, Swedish?

Reason I ask is because i hear impressive things re the Swedish systems from people with first hand experience, but not Australian. Record for most wire guided torpedoes 'in flight' is Swedish?
Only just saw this three years on, the combat system was a bespoke design developed by Rockwell, aided by Sperry Libroscope. Sperry took the money and ran leaving Rockwell, who had no experience designing submarine combat systems to try and fix something that was so ambitious that it likely still can't be done today. Boeing took over Rockwell and did their best to fix the mess, the entire thing eventually being replaced with the current BYG-2.

Sadly during the original selection the system used on the Walrus was recommended and rejected as not advanced enough, it was however, perfectly good enough and would have mitigated much of the technical risk that did so much harm to the project.
 
Submarines

To avoid detection by surface ships, in the mid-1960s Wallis proposed a fast, deep-diving submarine. The high pressures would be met by a novel Wallis hull structure based on several interconnecting cylinders of small diameter, rather than the single large cylindrical pressure hull used on contemporary (and modern) submarines. Propulsion would be provided by a closed-system gas turbine, the engine breathing liquid oxygen from tanks on board, and recycling the condensed exhaust gases back into the empty tanks. Both the hull form and propulsion systems were investigated in detail, but were not thought to offer significant advantages, and were not taken up.
1626801481851.png

 
Vanguard Class Boat 5: Right at the beginning of the Trident programme (1979) consideration was given as to whether the trident force should be four or five boats (with obvious parallels to the Polaris programme in the 1960s. In July 1980 the then Defence Minister (and direct predecessor to John Nott) Francis Pym said the following to the House of Commons:
The fifth boat was able to be abandoned because of the selection of Trident D5, which could carry an increased number of warheads. The Duff-Mason Report that argued in favour of the Trident programme actually considered as many as eight boats, to ensure three on patrol. Why three? Because some target sets required two boatloads of missiles, and there was concern about Soviet ASW capabilities. Three on patrol meant that one could be sunk in the runup to an exchange and the target set would remain fully covered.

Similarly, the five-boat force could maintain two boats on patrol, giving full coverage only if the boats remained undetected, but assured coverage of the less demanding target sets. Four boats could only assure one on patrol. It was thought likely, though, that in a period of escalating tension an additional boat could be surged to provide redundancy - giving three on patrol from a five-boat force, and two from a four-boat force. Theoretically, I suppose, the eight-boat force would allow a surge to four (maybe even five), though it's not discussed.

Duff-Mason initially dismissed D5 as it would 'exceed our needs, at high cost'. The selection of Trident D5 over Trident C4 was what swung it in favour of a four-boat force. Loading the D5 missiles with twelve re-entry bodies - not possible on C4 - would allow one boat to cover the most demanding target set, meaning that a fifth boat was not required. Using the Duff-Mason figures, a four-boat C4 force was about £1 billion cheaper over 20 years than a five-boat C4 force. It stands to reason that a four-boat D5 force must have been cheaper than a five-boat C4 force, though by a figure rather less than £1 billion.

A de-MIRVed C4 was considered, but came out about £1 billion more expensive than standard C4 with shorter range. This would be necessary if the US refused export licences for the MIRV system; it was felt that the UK would be unable to develop its own MIRV capability. Other alternatives thought feasible as alternatives to C4 were a UK-only 'Polaris A4' with major upgrades over Chevaline, and the French M4; Poseidon, like Trident D5, was considered only to dismiss it. Eight boats would be needed to achieve the required cover with A4, at a cost about 50% more than five boats with C4.

Also considered, then dismissed, was an SLCM-based deterrent. It was estimated that at least 400 missiles would need to be kept on patrol to service the most demanding target set, given likely loss rates. At 80 missiles per boat, this would require five boats on patrol, from a total force of eleven boats. As well as cost, the independence of this option would be severely undermined - it was felt that the US would be reluctant to provide unlimited access to the terrain database needed for mission planning, and that it would be prohibitive for the UK to develop its own. The only option would be for the UK to procure terrain data for defined routes from the US, which would constrain UK-only targeting options. Cost would be slightly more than the eight-boat A4 force, due largely to the cost of operating so many boats.
 

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