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Author Topic: Sentinel ACIV  (Read 31135 times)

Offline Abraham Gubler

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« on: November 26, 2009, 07:53:36 pm »
British tanks had the following turret ring diameters:
Cromwell - 60 in (1524 mm)
Comet - 64 in (1626 mm)
Challenger - 70 in (1778 mm)
Sherman* - 69 in (1753 mm)

And the Australian Sentinel ACIV tank with 17 pounder had a turret ring of 70” (1,778mm).
« Last Edit: December 04, 2009, 05:26:21 am by Jemiba »
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Offline JohnR

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« Reply #1 on: November 27, 2009, 05:33:37 am »
I have always been intrigued by the Sentinel, an amazing achievement when considering it was a design built from scratch in terms of design and engineering capability.  That they achieved a design that could take the 17pdr ahead of the UK is also amazing.

I have often wondered how it would have performed against German tanks?
« Last Edit: December 04, 2009, 05:26:35 am by Jemiba »

Offline Petrus

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« Reply #2 on: November 27, 2009, 06:19:50 am »
And the Australian Sentinel ACIV tank with 17 pounder had a turret ring of 70” (1,778mm).

I've read somewhere that when the Challenger was designed it was thought that minimum turret ring diameter allowing to mount the 17-pdr was 66in (1676mm).



Piotr
« Last Edit: December 04, 2009, 05:26:53 am by Jemiba »

Offline Abraham Gubler

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« Reply #3 on: November 27, 2009, 03:22:14 pm »
I have always been intrigued by the Sentinel, an amazing achievement when considering it was a design built from scratch in terms of design and engineering capability.  That they achieved a design that could take the 17pdr ahead of the UK is also amazing.

And in 1943 apart from preparing a 17 pounder armed version the Sentinel tank program was also running torsion bar suspension versions… So in 1944 they could have been producing something not far from the tank state of the art of the 1950s.

The key reason Australia was able to produce in the Sentinel a tank superior to what the British and the Americans were producing at the same time is the clean slate approach. Without the impost of established industry and their factories and established tank experts and their opinions the Sentinel emerged as the best that could be built based on war experience. While there were lots of critical shortages this often lead to some innovative solutions that may have been superior to the state of art. For example instead of a single high power engine clover-leafing together three engines enabling clutching in and out of engines as per power need and resultant lower fuel consumption, wear and tear (COPAP).

Also the start up Australian tank industry wasn’t as bad off in relation to workforce as people tend to believe. There were a few key engineers with lots of experience including a couple sent to the UK to learn tank building and a refugee French suspension expert. Also the rest of the workforce were all experienced train builders working in their workshops.

Back to turret rings. The original Sentinel Mks 1-3 had a 54” (1,370mm) turret ring. They were able to mount and fire the 17 pounder and even a twin 25 pounder used to simulate 17 pounder recoil before they were available. It was able to do so because turret rings are not actually a direct indicator of a turrets ability to mount and fire a gun. The turret ring just gives an indication of turret size if it has vertical walls (like most British and American tanks at the time).

The Sentinel had angled out and angled in walls so the turret volume and maximum diameter was actually larger than indicated by the turret ring. The Mk 4 Sentinel had a larger turret ring to improve this volume further and make it easier to elevate the 17 pounder and move ammunition from the hull to the turret (also to lengthen the tank to increase track surface area to keep ground pressure stable as the weight increased). Also the Sentinel program was producing far superior recoil absorbing mounts at the time. It was actually the Australian gun mount that was used for the Sherman Firefly to fire the 17 pounder.

I have often wondered how it would have performed against German tanks?

The Sentinel Mk 4 had a 17 pounder with 60 rounds of ammunition and 110 volt electrical turret traverse, a maximum speed of 56kph and a gross weight of only 32 tonnes. Glacis armour was only 51mm but highly oblique so presenting an actual thickness of 120mm to the horizontal. Turret walls was sub-standard at only 50-65mm but provided all round, but angled or layered to provide between 71-100mm to the horizontal. 510 Mk 4s were ordered for production (including 110 with interchangeable 25 pounder gun) to follow from 200 Mk 3s with 25 pounder. Only one tank of this full rate production following the initial batch of 65 Mk1s (2 pounder gun) was built.

More data at:

http://www.mheaust.com.au/Aust/Research/Sentinel/sentinelmk.htm
« Last Edit: December 04, 2009, 05:27:09 am by Jemiba »
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Offline JohnR

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« Reply #4 on: November 27, 2009, 04:35:58 pm »
Interesting read, thank you.

Regards.
« Last Edit: December 04, 2009, 05:27:22 am by Jemiba »

Offline Kadija_Man

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« Reply #5 on: November 27, 2009, 08:40:43 pm »
One of the developers of the Firefly was inspired by the AC3 "Thunderbolt" (with twin 25 Pdrs), after reading of its ability to withstand the recoil of the two guns fired simultaneously.  

Australia's real problem with the Sentinel was that it was completely inappropriate for the needs of the defence of Australia at that time.  The Army wanted to fight in Europe, not the Pacific and so decided they needed a tank capable of defeating the best the Germans had produced, rather than one which was needed to defeat the best the Japanese had produced.  In the end though, it was economics which saw it off.  A clear choice between producing aircraft and small ships or tanks and when it was obvious that tanks were available more cheaply and easier from overseas, the die was cast and the Sentinel was quietly put out to pasture.  Its only use in propaganda campaigns and a movie ("Rats of Tobruk" where the only unit actually equipped with them used them to portray German Panzers).  As technically superior as they might have been or become, the M3 Grant/Lee was the better vehicle on the grounds of economics.

I heartily recommend A.T. Ross' "Armed and Ready: Australian Defence Preparedness 1900-1945" for an excellent discussion about the problems of the Sentinel programme.
« Last Edit: December 04, 2009, 05:27:41 am by Jemiba »

Offline Abraham Gubler

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« Reply #6 on: November 27, 2009, 10:33:55 pm »
One of the developers of the Firefly was inspired by the AC3 "Thunderbolt" (with twin 25 Pdrs), after reading of its ability to withstand the recoil of the two guns fired simultaneously.  

They weren’t just inspired they obtained examples of the overhead short recoil system which was used as the technology base for the Firefly mounting.

Australia's real problem with the Sentinel was that it was completely inappropriate for the needs of the defence of Australia at that time.  The Army wanted to fight in Europe, not the Pacific and so decided they needed a tank capable of defeating the best the Germans had produced, rather than one which was needed to defeat the best the Japanese had produced.

That is totally wrong. The original requirement was to equip an armoured division to fight in North Africa as the British could not meet additional Australian demand for tanks. When the Japanese attacked the Australian armoured divisions (1-3) were re-rolled from training for North Africa for preparing to resist a Japanese invasion of Australia. The plan was to meet them with tanks and destroy them. The requirement for this role was something built in Australia because if the Japanese were invading then it’s unlikely that convoys of American and British equipment would have made it through and the Mk 1 Sentinel was all Australian.

After the victories of 1942 it was clear the Japanese couldn’t invade so the armoured divisions were disbanded and the domestic tank program halted. If Sentinel tank production had continued with the Mk 3 it would have been far better suited for fighting in the Pacific than the Stuart and Matilda tanks the Australian Army used.

In the end though, it was economics which saw it off.  A clear choice between producing aircraft and small ships or tanks and when it was obvious that tanks were available more cheaply and easier from overseas, the die was cast and the Sentinel was quietly put out to pasture.

Again more “common knowledge” which is equally wrong as the last statement. Sentinel production couldn’t compete with importing tanks from America. It was never an issue of building aircraft or ships or tanks. But rather domestic production competing with imports. As Australian labour was very short it was redirected from production of tanks and aircraft as these supply sources improved from our allies. n 1943 Australia cancelled production of the domestic Sentinel, the CA-15 fighter and the Woomera bomber. Much of the Sentinel industry capability went into supporting the huge fleets of landing craft that were flooding into the Pacific for use against Japan. Aircraft production continued at a reduced rate on other types but more so to retain industry capacity for post war use.
« Last Edit: December 04, 2009, 05:27:53 am by Jemiba »
"There is a tendency in our planning to confuse the unfamiliar with the improbable." Thomas Schelling

Offline Kadija_Man

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« Reply #7 on: November 28, 2009, 05:50:40 pm »
One of the developers of the Firefly was inspired by the AC3 "Thunderbolt" (with twin 25 Pdrs), after reading of its ability to withstand the recoil of the two guns fired simultaneously.  

They weren’t just inspired they obtained examples of the overhead short recoil system which was used as the technology base for the Firefly mounting.

They did not request the examples until after they had read about the "Thunderbolt's" ability to absorb the recoil of its twin 25 Pdrs on such a comparatively small turret ring diameter, Abraham.  Hence the use of the word "inspired".

Quote
Australia's real problem with the Sentinel was that it was completely inappropriate for the needs of the defence of Australia at that time.  The Army wanted to fight in Europe, not the Pacific and so decided they needed a tank capable of defeating the best the Germans had produced, rather than one which was needed to defeat the best the Japanese had produced.

That is totally wrong. The original requirement was to equip an armoured division to fight in North Africa as the British could not meet additional Australian demand for tanks. When the Japanese attacked the Australian armoured divisions (1-3) were re-rolled from training for North Africa for preparing to resist a Japanese invasion of Australia. The plan was to meet them with tanks and destroy them. The requirement for this role was something built in Australia because if the Japanese were invading then it’s unlikely that convoys of American and British equipment would have made it through and the Mk 1 Sentinel was all Australian.

After the victories of 1942 it was clear the Japanese couldn’t invade so the armoured divisions were disbanded and the domestic tank program halted. If Sentinel tank production had continued with the Mk 3 it would have been far better suited for fighting in the Pacific than the Stuart and Matilda tanks the Australian Army used.

Again, you miss the point, Abraham.  It was inappropriate because there was never any likelihood after December 1941 that any Australian armoured division was going to fight in North Africa.   Even if it had, taking yet another completely different type of tank to that theatre in such small numbers would have made it impossible to support the numbers required.  Finally, if the tank was intended to defend Australia against the perceived Japanese threat, then it was too heavy and heavily armoured to be easily deployable over the very poor transport system available (rather as the M1 Abrahms are today).  It would have been even worse in the SW Pacific.  The Mk. 3's only advantage over the Stuart and the Mathilda would have been its armament.  The Stuart was not used after the "Battle of the Beachheads" because of its light armour but the 'tilly was an excellent balance of protection, mobility and armament and so was the preferred vehicle in the SW Pacific (even after the M3 and M4 Mediums became available).  

Now, you may wish to live in some fantasy land where those factors were ignored but in real life they were the determinants, along with the real killer - the ease and cheapness of imported AFVs in the form of the M3 medium series,  which ensured that Sentinel programme was dismantled.

Quote
In the end though, it was economics which saw it off.  A clear choice between producing aircraft and small ships or tanks and when it was obvious that tanks were available more cheaply and easier from overseas, the die was cast and the Sentinel was quietly put out to pasture.

Again more “common knowledge” which is equally wrong as the last statement. Sentinel production couldn’t compete with importing tanks from America. It was never an issue of building aircraft or ships or tanks. But rather domestic production competing with imports. As Australian labour was very short it was redirected from production of tanks and aircraft as these supply sources improved from our allies. n 1943 Australia cancelled production of the domestic Sentinel, the CA-15 fighter and the Woomera bomber. Much of the Sentinel industry capability went into supporting the huge fleets of landing craft that were flooding into the Pacific for use against Japan. Aircraft production continued at a reduced rate on other types but more so to retain industry capacity for post war use.

Abraham, Australia suffered from a lack of manpower.  Indeed, it had over-committed itself to putting men into uniform to the point that units were demobilised in late 1944-early 1945 in order to keep the civilian economy working.   I wonder if you actually read what I said.  "Light ships", the last time I checked, included landing craft and indeed they made up a large bulk of what our shipyards produced.  It was a choice of either the light ships (Destroyers, Corvettes, Landing Craft, etc) and aircraft (Beauforts, Mosquitos, Beaufighters, Boomerangs, Wirraways, etc) or tanks instead of one of the preceding two.   The government decided it could import the tanks so discontinued the Sentinel programme.   Now Abraham, I named my source.  Can you please name your source(s) for these claims?
« Last Edit: December 04, 2009, 05:28:10 am by Jemiba »

Offline Abraham Gubler

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« Reply #8 on: November 28, 2009, 09:54:04 pm »
Ahh another wonderful ego + ignorance battle for all to behold…

 
They did not request the examples until after they had read about the "Thunderbolt's" ability to absorb the recoil of its twin 25 Pdrs on such a comparatively small turret ring diameter, Abraham.  Hence the use of the word "inspired".

So you agree that they weren’t just inspired they based their solution on the Australian technology. To leave it at just “inspired” would mean that the British heard about this great recoil absorbing system and then went off and did their own thing. Inspiration happens daily, building a new short recoil system enabling a high power gun to be fitted to a turret that previously only held a medium power gun happens very rarely, the difference is considerable. So give credit where credit is due and don’t just leave the role of Australian technology in the Sherman Firefly program as “inspiration” rather than the actual starting point. That is as misleading as not acknowledging the downunder involvement at all.

Again, you miss the point, Abraham.  It was inappropriate because there was never any likelihood after December 1941 that any Australian armoured division was going to fight in North Africa.   Even if it had, taking yet another completely different type of tank to that theatre in such small numbers would have made it impossible to support the numbers required.  Finally, if the tank was intended to defend Australia against the perceived Japanese threat, then it was too heavy and heavily armoured to be easily deployable over the very poor transport system available (rather as the M1 Abrahms are today).  It would have been even worse in the SW Pacific.  The Mk. 3's only advantage over the Stuart and the Mathilda would have been its armament.  The Stuart was not used after the "Battle of the Beachheads" because of its light armour but the 'tilly was an excellent balance of protection, mobility and armament and so was the preferred vehicle in the SW Pacific (even after the M3 and M4 Mediums became available).  

Ahh a subscriber to the gross weight theory of tank warfare… clear indication of someone who knows something more than a person on the street but not enough to be credible.

So what you are suggesting is in December 1941 the Sentinel tank program should have been abandoned and a new program started from scratch to build a lighter tank because clearly – as everyone knows – the Japanese only had light armour and anything over some undefined weight limit can’t be used anywhere near the Pacific Ocean? What a total load of crap.

The Sentinel was the best tank to defend Australia against Japanese invasion and it was the best tank to take the Pacific Islands back from Japan. And one doesn’t even need to assess its capability or mobility because it was the only thing domestically available within the timeframe. A tank that weighs 32 tonnes is better than a tank that weighs 0 tonnes.

As to the claim of poor transport systems this pretty much effects anything over a man portable load in the same way. Since the Sentinel only weighed 7 tonnes more than the Matilda (32 vs 25 tonnes) this would have made little difference. In the Australian defence scenario it’s a no argument.

Now, you may wish to live in some fantasy land where those factors were ignored but in real life they were the determinants, along with the real killer - the ease and cheapness of imported AFVs in the form of the M3 medium series,  which ensured that Sentinel programme was dismantled.

The Sentinel was more than suitable for the Australian Army mission in the war against Japan. It was far more suitable than any alternative both real and imagined. Of course it couldn’t compete economically with the imports but it was never cancelled because it was considered unsuitable. To try and generate this argument based on a fanciful concept of lead time required to build a tank, a lack of appreciation of the tanks role in defence of Australia warfare (not tank vs tank but tank vs infantry), attribution of awesome insight into the nature of all Japanese tank armour to the Australian Army and a magical belief that a certain gross weight makes a tank immobile; is an insult to the kind of appreciation of military technology that is the norm here at secretprojects.co.uk.

  I wonder if you actually read what I said.  "Light ships", the last time I checked, included landing craft and indeed they made up a large bulk of what our shipyards produced.  It was a choice of either the light ships (Destroyers, Corvettes, Landing Craft, etc) and aircraft (Beauforts, Mosquitos, Beaufighters, Boomerangs, Wirraways, etc) or tanks instead of one of the preceding two.   The government decided it could import the tanks so discontinued the Sentinel programme.  


No our shipyards did not produce many light ships, destroyers, corvettes, etc after 1943. Nor was the aircraft industry manufacturing those aircraft that you claim. The Beaufort and Boomerang programs were effectively over, Wirraway kept on for make work and Mosquito only starting up with most of it actually been done in the UK.

The workforce wasn’t needed for building ships or aircraft but supporting those that had been built, imported and operated near Australia by our allies. So industry like the Sentinel program converted to providing spare parts, repair and other supporting services to the huge fleets of landing craft and so on. It wasn’t as glamorous as building some of the best tanks or fighters in the world but it won the war which was the important thing.

 
  Now Abraham, I named my source.  Can you please name your source(s) for these claims?

I sincerely doubt you’ve actually understood anything in Ross’s “Armed and Ready” by the statements you’ve made above. But please feel free to make various references to other books that don’t support your arguments.
« Last Edit: December 04, 2009, 05:28:23 am by Jemiba »
"There is a tendency in our planning to confuse the unfamiliar with the improbable." Thomas Schelling

Offline Kadija_Man

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« Reply #9 on: November 28, 2009, 10:55:45 pm »
Ahh another wonderful ego + ignorance battle for all to behold…

At which point it would be better to leave it there, Abraham.  I see little further point in battling with both your ignorance and ego.   It is obvious you have only a superficial understanding and no experience of these topics.
« Last Edit: December 04, 2009, 05:28:41 am by Jemiba »

Offline Abraham Gubler

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« Reply #10 on: November 28, 2009, 11:48:40 pm »
At which point it would be better to leave it there, Abraham.  I see little further point in battling with both your ignorance and ego.   It is obvious you have only a superficial understanding and no experience of these topics.

Nice to see that even when you’re just typing insults you don’t want to deviate from your steady course of never letting a fact get in the way of a good opinion.
« Last Edit: December 04, 2009, 05:29:04 am by Jemiba »
"There is a tendency in our planning to confuse the unfamiliar with the improbable." Thomas Schelling

Offline Abraham Gubler

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« Reply #11 on: November 29, 2009, 12:03:07 am »
If Rickshaw’s attempts to rewrite Australian defence history is behind us perhaps we can return to the original question…

The design for Sentinel Mk 4 armed with an interchangeable 17 or 25 pounder had a turret ring of 70” but none of these tanks were actually built.

And the Australian Sentinel ACIV tank with 17 pounder had a turret ring of 70” (1,778mm).

The Australian War Memorial picture I attached in this original Sentinel turret ring post was not of a Mk IV but rather the E1. The E1 was a highly modified Mk 1 Sentinel that was used for trial mounting the 17 pounder. It was the famous tank with the turret with two 25 pounders mounted to simulate 17 pounder recoil (they actually generated 120% of the recoil).

The whole point of this post is the E1 had a 64” (1,624mm) turret ring. So it would be feasible to mount a regular 17 pounder on a Comet tank chassis with a new turret. But loading would be limited to a horizontal or depressed gun elevation.

For fans of the Sentinel here is what the Mk 3 or 4’s new hull front looks like with the removal of the hull gunner.
« Last Edit: December 04, 2009, 05:29:16 am by Jemiba »
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Offline JohnR

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« Reply #12 on: December 01, 2009, 03:34:44 pm »
Thats a big aesthetic improvement over the rather odd looking bow gunners, and I would imagine a considerable balistic improvement.

Regards.
« Last Edit: December 04, 2009, 05:29:30 am by Jemiba »

Offline Abraham Gubler

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« Reply #13 on: December 04, 2009, 04:13:55 am »
After another look at “Armed and Ready” Rickshaw is right that Andrew Ross does criticize the Sentinel as being “unsuited” for use against the Japanese. But he counters and qualifies his own argument a few times and his reasoning is very unsound (having spent quite a few years a decade or so ago serving on some committees with Dr Ross I don’t find this a surprise at all! Great guy but).

He points out that the original staff requirement for an Australian built tank in ‘40 was for something around 10 tons with minimal armour and able to counter Japanese light tanks. This was changed quite quickly to a medium tank able to fight German tanks after the Blitzkrieg in France. While Ross criticizes this decision it is heavily informed by hindsight. In 1940 Australia was at war with Germany and while the Japanese were considered a major threat all the planning to fight them was done so in the context of the Singapore and Bataan fortresses. The idea that the Japanese could defeat and advance past the UK and USA forces into SE Asia and the SW Pacific was considered ludicrous before they did it. In this context the land fight against Japan was seen as fighting them off from fixed positions and the need for a light anti-Japanese tank is a poor second to the medium anti-German tank.

Ross’s main criticism of the Sentinel program is that after the Japanese attack the Army kept asking for improved weapons (17 Pounders) to fight the Germans when 2 Pounders were adequate for defeating Japanese tanks. While this argument is on more solid ground it doesn’t take into account that the Australian Government made a commitment to retain a division in the European theatre until the end of the war and said division would require tanks (just like the equivalent NZ division). It was only after the loss of an Australian division in Singapore and Java thanks to poor British command that the European division was recalled to Australia and the policy changed (even then it stayed until after El Alemein).

Ross agrees that the Sentinel Mk 3 with 25 pounder was the best suited tank to fighting the Pacific campaign against the Japanese. He still remains critical of its medium size but this thick armour would be crucial for its survivability and didn’t appear to be a production bottleneck for the Sentinel. The cast armour by Bradford Kendall Ltd (still casting steel today) was one of the success stories of the program and enabled rapid design evolution compared to jigged welding or bolting production.

Japanese anti-tank tactics may not have used big guns but were sufficient to require medium tanks and clear light tanks from the battlefield. Because of the close terrain their 20mm anti-tank gun was extremely lethal against light tanks and their heavy use of mines and suicide command detonated explosives required strong protection. The Sentinel with its thick castings of softer but tougher steel alloy made it very resistant to spalling from blast effects.

As to the difficulties of moving a 30 ton tank into the SW Pacific battlefield they aren’t much more difficult than moving a 10 ton tank. Once on the ground the difference is minimal (thanks to equal ground pressure) and with no such thing as local bridging this is not an obstacle. A US Army study in the mid 1960s found that 50% of South VietNam was accessible to main battle tanks (50 tons). Which is amazing considering a quarter of South VietNam is the Mekong river delta impassible to any weight bearing vehicle and another third is the central highlands a thickly forested mountain range.

PS Perhaps a moderator should split a lot of this off to a separate Sentinel thread?
« Last Edit: December 04, 2009, 05:29:44 am by Jemiba »
"There is a tendency in our planning to confuse the unfamiliar with the improbable." Thomas Schelling

Offline Abraham Gubler

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« Reply #14 on: December 04, 2009, 04:17:27 am »
Thats a big aesthetic improvement over the rather odd looking bow gunners, and I would imagine a considerable balistic improvement.

Its a very well shapped tank. The strange looking bow gunner ball in the Sentinel Mk 1 was influenced by the use of Vickers .303 MG. Since Australia didn't have BESA or 7.92mm production they had to use the Vickers with the barrel shroud.

Here are pictures of the side and rear of the Mk 3. The turret ring is actually in a depressed section surrounded by bulwarks so any shot can't hit it directly.
« Last Edit: December 04, 2009, 05:29:58 am by Jemiba »
"There is a tendency in our planning to confuse the unfamiliar with the improbable." Thomas Schelling