Sea Slug

zen

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On quick check it seems we don't have a thread on Sea Slug and it's development.

Often people mention a inline boosted option instead of the wrap around boosters.
Yet I seem to recall that there were worries over rocket gases causing problems with the beam rider guidance.

Would be nice to know if there's anything more on this weapon. Beyond BSP series that is....
 

sferrin

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I'm fairly certain I've seen the in-line Sea Slug around here somewhere. ???
 

zen

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sferrin said:
I'm fairly certain I've seen the in-line Sea Slug around here somewhere. ???
I've only seem NIGS.
 

Grey Havoc

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sferrin said:
I'm fairly certain I've seen the in-line Sea Slug around here somewhere. ???
I have the strange feeling I've seen it as well.
 

zen

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I am given to understand that there is a drawing available in the library at HMS Collingwood. If I can get access and the time Portsmouth is not too far away or expensive for me.
But what worries me is that it's likely to be NIGS
In a way on pondering this cleaned up version of Sea Slug, it's quite clear how easy it would be within the limitations of the missile's body to fit a SARH seeker and how it could all quickly spital out of control into bleeding edge technology of NIGS.

Which is a shame as a more limited and evolutionary development of Sea Slug would have reaped rewards for further incremental improvements.

Anyway Sea Slug seems to go back to LOP/GAP during WWII and Long Shot?
We have here somewhere a hardened SAM system for land called Thunderbird but it depicts a missile looking exactly like Sea Slug.

At what point did work on a linear booster stop?
 

CJGibson

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I think there was a proposal to put a tandem boost on Sea Slug when the County-class destroyers were sold to Chile, but that's a vague recollection.

Chris
 

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zen said:
Often people mention a inline boosted option instead of the wrap around boosters.
This is mainly length vs diameter trade. Britain considered length more important than diameter, but since plans to install "Sea Slug" on retrofitted missile cruisers & frigates were scrapped, and "County" were build specifically around "Sea Slug" system we could not establish, were they right or wrong. If the plans for "Sea Slug"-carrying escorts came into fruition in late 1950s, then, probably, the compact size of "Sea Slug" would become great advantage.

Also, the all-forward booster arrangement allowed to use relatively small fins during launch, and (theoretically) made missile more reliable. Since all four boosters were aligned such that their thrust was concentrated in single point, one booster failure would not led to failed launch - the other three would manage without destabilizing the whole missile.
 

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I am glad that there is now a specific Seaslug thread.

Apart from the US Navy only the Royal Navy deployed a first generation SAM of domestic manufacture on 4 destroyers.
The only other comparable system was France with its Masurca, deployed initially on similar destroyers (Suffren and Duquesne) and then on a converted cruiser (Colbert).
Masurca was also planned for the helicopter training ship Jean D'Arc, which resembled the planned RN Escort Cruiser.

The US Navy's comparable system was Terrier (Later Standard), which deployed initially on the Coontz class destroyers. These ships are the closest analogue to the County DLGs in RN service.

Terrier was fitted to Italian Escort Cruisers (2 Doria Class and 1 Vittorio) and a converted wartime cruiser (Garibaldi) as well as a Dutch missile cruiser (Zeven Provinzien).

Eventually, Seaslug was fitted to 8 Countys (though its Seaslug 2 version seems never to have been formally accepted into service).

The proposed Escort Cruiser design for the RN was soon re-designed to take CF299 (Seadart) and DLGs 9 and 10 of the County Class were cancelled.

Refitting CF299 to the Countys was a non-starter because of the vertical storage arrangement coupled with the high manopower costs of the Countys. In an ideal world CF299 would have come into service in the late 60s and the Countys would have given way to 4 Escort Cruisers and 8 Type 82s with CF299, plus a number of simpler CF299 single arm launcher ships.

On the whole, the RN did better than the RN as Seaslug was more capable and reliable than Terrier and Seadart was more capable than early Standards. AEGIS and developed Standard altered the picture
 

zen

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Interesting site here.
http://www.littlewars.org.uk/Seaslug/seaslug03.html
 

sferrin

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uk 75 said:
I am glad that there is now a specific Seaslug thread.

Apart from the US Navy only the Royal Navy deployed a first generation SAM of domestic manufacture on 4 destroyers.
The only other comparable system was France with its Masurca, deployed initially on similar destroyers (Suffren and Duquesne) and then on a converted cruiser (Colbert).
Masurca was also planned for the helicopter training ship Jean D'Arc, which resembled the planned RN Escort Cruiser.

The US Navy's comparable system was Terrier (Later Standard), which deployed initially on the Coontz class destroyers.
Don't forget the earlier Terrier conversions.
 

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Tandem Booster Sea Slug - From memory, at the time (or shortly after) the Counties were sold to Chile the boosters, a product of BAJ, who no longer existed, where found to be suffering from corrosion between the case and the charge. A proposal was made to replace the four boosters with a single Sea Dart Chow booster which was in production at ICI Summerfield. I can’t remember if it was a standard Chow or a development there of. I don’t know if this progressed beyond a proposal to hardware, suspect not, but would like the know for sure.

The Sea Darts Chow had at least in part, a composite propellant which contained aluminium. This caused problems for salvo launches because the efflux cloud (think chaff) from the first launch produced radio interference problems which adversely affected the second..... it’s not easy to make these things work.
 

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Zootycoon said:
I can’t remember if it was a standard Chow or a development there of. I don’t know if this progressed beyond a proposal to hardware, suspect not, but would like the know for sure.
I'm not sure it's even possible. Even without boosters, "Sea Slug" is almost two time heavier than "Sea Dart" (898 kg vs 544 kg). A single "Chow" booster with 35000 lb thrust wouldn't be able to do the job of four 27800 lb "Goslig".

Not to mention, that it would create the enormous problems with missile stability during boosting, since the center of gravity would be completely out of place. And the tail-booster configuration would require large fins for boosting phase - and such fins simply wouldn't fit in launcher. Let's not forget, the "Sea Slug" used internal placement of missiles inside the launcher frame.
 

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You’re;-
1 quoting the missile weight included the booster/s;- from memory a Sea Dart without the booster was less than 200kg. I’ve no idea what the weight of the Sea Slug without boosters but if you assume a similar mass fraction it would be about 300-350Kg;-
2 Quoting booster peak thrust;- in both types this only occurs briefly, the Gosling (not convinced they were Gosling;- that was Booldhound/Thunderbird and was much longer but same principle ) were cigarette burning double base charges which suffer a big thrust drop as the combustion volume opens up. The Chow was far more sophisticated;- both double based and composite charges in the chamber arranged to give an I initial kick then a period sustained thrust. Although I don’t have the figures, I suspect the Chow would have a higher Isp.

Anyway 35000lbf (15 Tons) peak thrust with it burning for 2.2 sec would get 350Kg flying (@24 g), its initial weight would be in the region of 600-650 Kg which add a little, no blunt faced draggy boosters, but maybe it wouldn’t make the same range as the original.

Yes, it would need the additional tail fins, at least, integrating this into the missile, the launcher, the guidance/control system requires a fair bit of modification and all this would need extensive trials, very expensive work to boot;- all that’s true what ever the tandem booster looks like.

I quite distinctly remember the Chile Sea Slug Chow proposal mentioned once during a presentation but it was never mentioned again. Given the size of the project had it gone live, I’m sure I would have picked something up but you could never quite tell.
 

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When comparing a tandem booster to the wrap around you must consider net thrust (booster thrust minus its drag) not absolute. In the tandem arrangement the booster represents only a tiny fraction of the center body drag so close to 100% of its thrust accelerated the mass mass against its drag. The wrap around boosters have flat noses to ensure they spread correctly at separation. This means the booster itself generates a lot of drag. Hence most of the booster thrust is simply pushing against its own drag.

The Sea Slug booster arrangement is an incredible inefficient way to launch anything
 

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Again posted in error;- a small modification is resulting as a new post
 

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Zootycoon said:
You’re;-
1 quoting the missile weight included the booster/s;- from memory a Sea Dart without the booster was less than 200kg. I’ve no idea what the weight of the Sea Slug without boosters but if you assume a similar mass fraction it would be about 300-350Kg;-
Er... The TOTAL weight of Sea Slug with boosters is about two tons. Each Gosling booster weighted about 300 kg.

Zootycoon said:
from memory a Sea Dart without the booster was less than 200kg.

but if you assume a similar mass fraction it would be about 300-350Kg;-
You would not assume, because Sea Dart is powered by air-breathing ramjet, and Sea Slug is powered by solid rocket sustainer motor. The Sea Slug is much heavier, because it transported all its fuel, propellant and oxidizer on itself, while Sea Dar took a large portion of propellant and all oxidizer from air.
2 Quoting booster peak thrust;- in both types this only occurs briefly, the Gosling (not convinced they were Gosling;- that was Booldhound/Thunderbird and was much longer but same principle ) were cigarette burning double base charges which suffer a big thrust drop as the combustion volume opens up. The Chow was far more sophisticated;- both double based and composite charges in the chamber arranged to give an I initial kick then a period sustained thrust. Although I don’t have the figures, I suspect the Chow would have a higher Isp.
They were Gosling; there were no other available before Retriever appeared.
Anyway 35000lbf (15 Tons) peak thrust with it burning for 2.2 sec would get 350Kg flying (@24 g), its initial weight would be in the region of 600-650 Kg which add a little but maybe it wouldn’t make the same range as the original.
Again: you need to move about 850 kg of Sea Slug weight & accelerate to supersonic speed, because otherwise the missile control system would fail.

Yes, it would need the additional tail fins, at least, integrating this into the missile, the launcher, the guidance/control system requires a fair bit of modification and all this would need extensive trials, very expensive work to boot;- all that’s true what ever the tandem booster looks like.
Basically, it would be cheaper to just build a new missile.

Must admit, that I toyed with the idea of improving Sea Slug for some of my alternate history project, but the best I could suggest was to install infrared terminal guidance by employing Red Top seeker & homing on target from the dive. And it would require fairly extensive rebuild of the missile.
 

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The mystery of how Chile supported it Sea Slug is revealed;- The book “Summerfield The history of a rocket research establishment” by Hugh Nicholson tells us on page 36

“Counties, two of which had the Seaslug system installed. As they required the system to remain in service for a considerable period the Chileans requested information on residual motor life and also possible refurbishing techniques. Summerfield had prefected a technique whereby the propellant could be removed from the casing by a combination of machining and high pressure water jet. The casings was then refurbished and new propellant case bonded. This technology was made available to Chile and assistance was given in setting up the necessary facilities for doing this work in there country”

As I suspected, the Tandem booster SeaSlug was probably a design proposal which was stillborn due to high cost and superseded by establishing an effective refurbishment capability.

Page 35 includes a detailed description of the development of the SeaSlug’s RETRIEVER Boosters. The problem encountered inservice was after a few years a variation in burn rate developed which and lead to uneven booster separation.
 

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Recalled some interesting data about Seaslug unusual design. Apparently, Navy preferred short, horizontal-stowed rocket, because officers were concerned about the possibility of reloading system faliures in combat - either because of recieved damage, or mechanical malfunction.

The compact, stubby Seaslug could at least theoretically be manhandled, put on trolley and loaded into launcher by hands. This was one of the reason, why RN decided against Terrier missile - its lenght and (initial) vertical storage made nearly impossible any manual handling at all.
 

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Sea Slug in action.

https://www.youtube.com/watch?v=_ULvSrslNbo&feature=youtu.be
 

zen

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Perhaps we should also consider Long Shot which was supposedly a previous SAM and AAM effort and was two stage.
 

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There may be a number of reasons for using wrap-around boosts.

1) No single boost rocket motor with sufficient power, so need more than one. (see early test vehicles with up to eight BRMs)

2) With wrap-around boosts your missile can be as big as you like, just add BRMS,

3) Asymmetric thrust if one BRM fails? No problem, cant the nozzles so the thrust lines pass through the missile CoG. This may also make the missile easier to control in the boost phase, should you want to.

Chris
 

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From Down South by Chris Parry detailing his time on HMS Antrim.

“The Sea Slug was the only anti aircraft missile that could shoot itself down” reference to its unfortunate habit of colliding with its boosters at/after separation.

The mk2’s boosters had multiple radial bands along it length for further destabilisation but I don’t think even this was a satisfactory fix.
 

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zen said:
I am given to understand that there is a drawing available in the library at HMS Collingwood. If I can get access and the time Portsmouth is not too far away or expensive for me.
[snip]
At what point did work on a linear booster stop?
There is indeed a drawing in the CHC library; unfortunately there is nothing else. I'd guess it makes the missile at least 30 feet long though.... I don't think it ever went any further than a vague proposal.
 

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uk 75 said:
I am glad that there is now a specific Seaslug thread.

Eventually, Seaslug was fitted to 8 Countys (though its Seaslug 2 version seems never to have been formally accepted into service).
I'm glad Seaslug has its own thread too!

Seaslug Mk2 definitely did enter service; I was supplying them to the ships in the eighties. I can't help feeling that these rumours were started by the USN to scupper any chances of Seaslug exports.
 

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Zootycoon said:
As they required the system to remain in service for a considerable period the Chileans requested information on residual motor life and also possible refurbishing techniques. Summerfield had prefected a technique whereby the propellant could be removed from the casing by a combination of machining and high pressure water jet. The casings was then refurbished and new propellant case bonded. This technology was made available to Chile and assistance was given in setting up the necessary facilities for doing this work in there country
While the Chileans were purchasing the ships IMI Summerfield pointed out they still had a batch of casting powder. This was sold to them and I had to send batches of old Retriever motors to be washed out and re-filled.! It was an awkward process as Summerfield had to arrange the deliveries with the police as the access was through Kidderminster town centre; roads had to be closed and the single RN Bedford lorry escorted through!
 

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Zootycoon said:
From Down South by Chris Parry detailing his time on HMS Antrim.

“The Sea Slug was the only anti aircraft missile that could shoot itself down” reference to its unfortunate habit of colliding with its boosters at/after separation.

The mk2’s boosters had multiple radial bands along it length for further destabilisation but I don’t think even this was a satisfactory fix.
With all due respect to Chris Parry I've never come across an incident of a Seaslug hitting its own boost motors. It may well have happened during the trials at Woomera or Aberporth (which is what these trials were for) but not during continuation firings unless someone changed the salvo interval, which was set at 6 seconds to stop that very thing happening.

The 'radial bands' are the spoiler rings; they are there to provide drag when the boost motors are released so by the time they have rotated they are behind the missile.
 
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