TOG Amphibian

United Kingdom (1940)
Amphibious Tank – Design Only

The Old Gang (TOG) was an informal and perhaps derogatory name applied to the men who had been primarily responsible for delivering British tank designs in WW1. With a new war started in 1939, these men, under the leadership of Sir Albert Stern, were formed into the Special Vehicle Development Committee (S.V.D.C.), although they soon adopted the TOG moniker as a badge of honor. More commonly known for work on the large heavy tank projects TOG-1 and TOG-2, the SVDC were actually a body utilised for their expertise for a number of projects and one of those, in the Summer of 1940, was the need for an amphibious tank.

With a flair for design and the ability to work unencumbered by the normal military and political bureaucracy, the SVDC delivered one of the most unusual ideas for an assault tank of the war – one which approached the enemy from under water.

Background

On 30th July 1940, Mr. Burton, the Director General of Tank Technology (D.G.T.T.), approached Sir Albert Stern to request S.V.D.C. assistance in solving two tank design questions: a tank suitable for an airborne invasion, and a tank for a seaborne invasion.

General Pope, the Director of Armoured Fighting Vehicles (D.A.F.V.) had actually issued the original requirements for an amphibious tank back in March and clearly, the task was so difficult that the S.V.D.C.’s help was now being sought. This difficulty is hardly a surprise given the almost utter absence of any work on amphibious or wading of tanks in the preceding decades, asides from some like the Mk.V and VI Light Tanks, and of course the minuscule Vickers-Carden-Loyd Amphibian (A.4E12). All of these were vehicles which were barely bulletproof and utterly useless for any invasion of the French mainland with an opposed amphibious landing against a prepared enemy.

This need for an amphibious tank was less obvious in March 1940, when it was ‘something we might want’, as opposed to a post-Dunkirk point when the British had been pushed off continental Europe. Any new attempt to bring a land war against Germany in France would guarantee the need for an amphibious landing and this would have to be led by tanks. The small problem was that virtually no work had been done on the subject and there was no suitable vehicle available.

“the War Office considers it very important that an amphibian tank should be developed to meet modern requirements… It seems to me that this is a problem that might well be studied by your Committee, and the scheme developed possibly up to the stage of making pilot models… the development of an amphibian tank of real use is a matter of great importance.”

Letter from Sir Albert Stern to Mr. Burton, dated 9th August 1940

On 9th August 1940, Stern wrote back to Mr. Burton agreeing that the S.V.D.C. would assist in the design of an amphibious tank and that they would need £100,000 for the production of a pilot model.

Sir Albert Stern Stern invited Mr. Burton and General Pope to meet directly with the SV.D.C. on 12th August to discuss the exact requirements for this amphibious tank. General Pope, however, was unable to attend but forwarded to them the requirements as document ‘Specification 1.A Amphibious Tank Operations’ with the clear goal “to land tanks on an open beach in the face of enemy resistance and to gain a bridgehead 3 to 5 miles [4.8 – 8.0 km] deep to cover the landing of other troops”, certainly no small requirement.

The S.V.D.C. were to be tasked with investigation of a design which could be launched 200 yards (183 m) from the beach and navigated to shore above or below water if necessary and both of those options came with advantages and disadvantages alike. There was even the possibility of considering “fitting the necessary tracks and armour to a boat with some sea going powers but limited cross country performance” although the obvious impracticalities of such an idea were as apparent then as they are now. The S.V.D.C.-designed amphibian would have to be designed, trialled, and approved, and built in large numbers to be available by 1st April 1941 – less than a year away!

Armor was not going to be ignored as it had on the very limited attempts at amphibious tank work beforehand. This vehicle would have to be proof against all enemy small arms fire, including armor piercing bullets at normal impact at all ranges as a minimum. Further, the front of the tank should be able to resist the German 37 mm gun at normal impact at 300 yards (274 m). Armament, as dictated by General Pope’s requirements, was not the 6 pdr. Stern had been looking at the venerable 2 pounder. This was obviously going to be a disappointment in terms of not getting the bigger gun mounted but was a logical move given the incredibly tight time constraints needed. Adoption of a known and proven gun meant a lot of savings in development time. Alongside this gun was to be a 7.92 mm Besa machine gun and both weapons were to be mounted in a turret. Interestingly, there is no mention at all of a hull-mounted weapon of any kind.

Crewed by 3 men, a commander, gunner, and a driver, the tank would have to be able to manage 8 – 10 mph (13 – 16 km/h) on land cross country and negotiate water (either above or below the waves) at 4 knots (7.4 km/h).

Dimensions of the tank would be somewhat dictated by the need to cross trenches and climb steps but these requirements were far below those set for the other TOG tanks back in September 1939. This time, the need was to cross a gap 5’ 6” (1.7 m) wide and a step just 3’ (0.9 m) high. The vehicle would only need a range of operation of 50 miles (80 km) but would have to be able to climb up wet, loose, shingle beaches and be “capable of operating under tropical and European conditions”. The inclusion of a No.11 wireless set (or equivalent) as well as an inter-troop radio set completed the needs identified by the Army for the tank.

By 19th August, just 10 days after receiving the order, the SVDC had finished their design whilst still working on TOG-1, a new hydraulic system for TOG-1A, and the new primary heavy tank TOG-2, amongst other work.

The SVDC surmised the amphibious tank into 3 key considerations. Firstly, it had to be ready for action the moment it got to the beach – there would be no time to shed buoyancy packs or screens. Secondly, it would have to be immune to enemy fire, including strafing or bombing by enemy aircraft during the water phase of the assault and be as light and small as possible. Thirdly, by making the vehicle as small as physically possible, the armor requirements would likewise be kept as small as was possible whilst still meeting the requirements for protection which had been set. When Stern released the SVDC designs of the tank, it was to be 18’ 9” (5.7 m) long and just 7’ 9” (2.4 m) wide with the hull an incredibly small 3’ (0.9 m) high.

Accounting for a ground clearance of just 15” (0.38 m), this would mean that the top of the hull would be a mere 51” (1.3 m) from the ground. The driver would likely have to be lying a little supine in order to fit. What this tight design would do was to keep the weight to just 14 tons (14.2 tonnes) (plus or minus 10 %) (12.6 to 15.4 tons / 12.8 to 15.6 tonnes). The design produced was a tank which was only slightly lighter than the 16-ton (16.3 tonnes) Valentine (Infantry Mk.III) tank which also mounted a 2 pounder gun and was a little shorter than this vehicle. It proved to be unsuitable for amphibious wading.

“war should not be handled in this way.”

Report of Interview between Sir Albert Stern and Herbert Morrison, dated 3rd September 1940

Work continued through 23rd August with General Pope still adamant on the need for an amphibious tank and it was one of three topics of discussion at a meeting held on 3rd September 1940 and also to discuss the growing rift between Sir Albert Stern and Mr. Hopkins, the Director of Naval Land Equipment (N.L.E.). The N.L.E. felt out of sorts that the S.V.D.C. had been tasked with designing a tank to operate at sea, when the sea was something they felt was in their domain.

Yet, at the same time, Mr. Hopkins was perfectly happy to be carrying on a programme of development of an enormous trench digger which took engines from the S.V.D.C.’s own projects, having no qualms about his Department developing a land-based vehicle.

It is hardly any wonder that efforts at a high level took place to keep Mr. Hopkins away from meetings where Sir Albert Stern was going to be present, likely to protect him from the critique of that hypocrisy which would be inevitable. The split in the relationship of the two was not helped by the decision by Mr. Burton in September to strip from the S.V.D.C. of the role (still officially unofficial) of design responsibility of the amphibious tank and hand it to Mr. Hopkins at the N.L.E. telling Stern to “give out advice” – an optimistic sentiment all things considered and a slap in the face of Stern and the S.V.D.C. who had completed their design. With the obviousness that Stern would not work like that, Mr. Burton did eventually relent and agreed that the N.L.E. and S.V.D.C. should work together on the design and produce a working model.

That issue, amongst others connected with the other TOG designs, only served to illustrate and prove Stern’s point to Mr. Morrison that there was a need for a separate body solely in charge of tank design. A point he omitted no chance to press for and would not get. S.V.D.C. work officially ceased on 10th September 1940, all work was to go to the N.L.E. instead although the N.L.E. did continue to use the expertise of Mr. Ricardo for his engine expertise for some time afterwards.

Under the Sea

The biggest difference between this SVDC vehicle and preceding designs was going to be that this vehicle was not going to try and float, but drive on the sea floor instead. The logic for this decision was as simple as it may be initially counter intuitive. Whilst on the surface, on pontoons or with a screen (like a Straussler system), a tank would be visible to the enemy the entire time and unable to fire back. At the mercy of enemy gunnery, casualties could be inflicted even before they reached the beach, at which point the encumbrance of the floatation equipment would be a big problem. Indeed, in 1940 this had not yet been overcome with Straussler equipment, explosive removal of wading equipment and waterproofing compounds to seal the vehicle.

The 1940 solution for the SVDC was both unusual and innovative in that, whilst on the seafloor, the tank would be completely immune to enemy fire and be able to rise out of the water at the surf instantly ready to fire on the surprised enemy watching these poseidon-esque vehicles rising from the depths.

On the sea bed, the tracks would be able to engage with the sand and shale at a higher speed than on the surface without worrying about a rip tide or breakers. In fact, the SVDC estimated a sea floor speed of 6 knots and, at the same time, completely removed the complications of a propeller or the as-yet-to-be-designed steerable water jets from Messrs. William Foster and Co. As the vehicle was in contact with a tractable surface (sand and shale of the beach) there were no worries about the vehicle becoming trapped in the surf onshore, as could easily happen with a floating tank with little purchase on the beach at this key point. A large vulnerable floating target therefore stranded on the foreshore like a whale could be avoided by just being underwater could the equal risk of becoming damaged on the way to shore with a pontoon becoming holes and the tank capsizing or sinking.

The obvious question over an underwater vehicle is the problem of keeping water out, however this is not as big of a problem as may be imagined. With a submersion duration of just 3 minutes, a small bilge pump capable of pumping 30 gallons (136 litres) per minute against a head of 25 ft. (7.6 m) of water was more than adequate for the task. The next obvious problem is air for the crew and engine. For the engine, this was provided for with tanks of compressed air and for the crew by simply battening down the hatches to prevent air escaping. There was plenty of breathable air inside the volume of the hull and turret for the time submerged. It is not that there was no time for escape either. Designed for submarines, the Davis Escape Apparatus was already available in 1939 and, by 1944, the Tank Underwater Escape Breathing Apparatus would also be widely available. That piece of kit provided up to 7 minutes of oxygen for each crew man to get to the surface of the water in case of a problem requiring escape.

Navigation underway was to be aided by means of a spot lamp on the turret and a compass, although it was accepted that submerged rocks might be a problem for which there was no easy solution, although most of the large ones had already been well charted.

Deployment

In order to protect the vehicle during the water phase of the assault, Sir Albert Stern, a man who was himself an amateur sailor with some experience in boats, proposed the use of a large ship to deliver the tanks. That ship would have to have a draft of at least 18 to 20 feet (5.5 – 6.1 m) and launch the tanks into water about 25 feet (7.6 m) deep via a ramp. As many tanks as possible should be packed onto that ship to maximise the weight of tank-force being delivered to the shore and this, with the ship size, meant deploying up to 600 yards (549 m) from shore instead of 200 yards (183 m).

In an October 1940 report, Mr. Ricardo suggested a suitable ship as a repurposed whaling vessel about 10,000 to 20,000 tons (10,160 to 20,320 tonnes) in weight, as they had ramps capable of dealing with whales weighing 80 to 100 tons (81 to 102 tonnes) and could launch “several hundred small submersible tanks” very quickly.

Armor

The TOG amphibian had to be proof against all enemy small arms fire including armor piercing bullets at normal impact at all ranges as a minimum. In addition to this, the vehicle should ideally be able to resist the German 37 mm gun at 300 yards (274 m) at normal impact although absolute immunity was accepted as unattainable for the tank.

To meet these needs, the first step was to make the tank as small as possible so as to present the minimum possible target to the enemy.

On top of that, armor not less than 2 ½” (63.5 mm) was proposed on the front, although 2” (50.8 mm) would probably be sufficient if needs be, especially where normal impact was unlikely. Side armor was to be substantially thinner, just ⅞” (22.2 mm) thick and with floor and roof plates between 3/8” and ½” (9.5 to 12.7 mm) thick.

Automotive

The primary manufacturer for pilot models for the S.V.D.C. was Messrs. William Foster and Co. of Lincoln and they had no experience in building amphibious vehicles. They did, however, have experience building barges for the Admiralty. Those barges were specifically designed to obviate the need for propellers for propulsion, as a propeller would be damaged by hitting a beach. The same sort of thing was going to be true of this tank design and the solution offered was to be the same too. If the tank was going to float, it would use jet propulsion instead of a propeller, even though the lack of a keel made those barges hard to steer and this would be the case with a floating tank too. The solution was to create a new design of a steerable jet instead.

Ground clearance was to be 15” (0.38 m) and the tank would run on tracks 18” wide producing a ground pressure of just 6 lbs. sq. in. (41.4 kPa). This very low ground pressure would assist in the obviously saturated ground it would have to drive on under the water but the bigger problem of being underwater was buoyancy.

Buoyancy was obviously essential if you wanted to float but here the important part was to not be buoyant. Floating was to be avoided and buoyancy was a function of the mass of water displaced. This tank was to weigh 14 tons (14.2 tonnes) so, if it displaced more than 14 tons (14.2 tonnes / 14.2 m3) of water, it would float.

The S.V.D.C. calculated the actual buoyancy of the tank as just 8.5 tons (8.6 tonnes), meaning that the effective weight of the tank when submerged was just 5.5 tons (5.6 tonnes) reducing the ground pressure to an incredible 2.5 lbs.sq.in. (17.2 kPa). Bearing in mind an average human exerts a pressure of about 8 lbs.sq.in. (55.2 kPa) reducing this to just 2.5 lbs.sq.in. (17.2 kPa) was exceptional.

A lesser-appreciated problem of running a vehicle underwater is that of engine cooling. With the engine compartment having to be sealed off during transit, the radiators would be out of action and this meant that the cooling would have to be able to work with a high water temperature, something which ruled out the possibility of simply cooling the engine with sea water.

This issue was resolved by use of a heat exchanger arranged in series with the radiator so that a fresh water cooling system could be retained, which could be the primary cooling on land. When submerged, the air intake shutters could be closed to keep sea water out and have the heat exchanger dump the engine heat to the external sea water. Even less of a problem was the exhausting of gases from the engine. Even against a head of 20 ft. (6.1 m) of water, the engine exhaust could comfortably bubble out the gas, although this would cause large bubbles on the surface of the water (the bubbles will expand on their way to the surface courtesy of Boyle’s law). If complete secrecy was needed, then these bubbles bursting out on the surface of the water could be disguised by means of a simple canvas pipe from the exhaust pipe of the tank to the small float on the surface. As soon as the tank surfaced on the beach, the canvas tube would drag behind and rapidly burn off from the heat, removing the need for someone to get out to take it off.

Air for the engine was to be provided for by one of two possible solutions. The first was the use of a 3” (76.2 mm) diameter telescopic tube to the surface of the water, but this was vulnerable to damage. The alternative, and the solution which was selected, was provided for by means of compressed air. It was calculated that the effort of driving the tank in the water-medium instead of air would waste 50 hp of the engine, so that 5 knots was the realistic submerged speed. At that speed, it would take 3 minutes to reach fresh air and, with the engines consuming around 1.3 cu. ft. (3.68 x 10-3 m3) of air per hp. per minute, a 3 minute journey would require 200 cu. ft. (5.66 m3) of air. In order to allow a margin of safety, two 400 cu.ft (11.3 m3) cylinders would be fitted, providing a 4:1 safety factor. With the engine power wastage through water and at the sprocket (an additional waste of 0.5 hp per ton per mph) and with a mechanical transmission efficiency of around 80%, the minimum engine size of 70% in an ideal world would actually would have to be 87.5 hp, which led the S.V.D.C. to decide an engine of not less than 90 hp was needed.

In considering an engine, there were two options. The first was a Ford V8, and the second was an engine from Vauxhall Motors, as used in the Bedford lorry. Both could produce the 90 hp required from 67 octane petrol but would also consume more air than previously planned for, specifically around 350 cu. ft (9.9 m3) of air for that 3 minutes of submerged driving. The adoption of the two 400 cu. ft. (11.3 m3) air tanks would still be sufficient and reduced the margin of safety from 4:1 to just 2.25:1.

Of the two engines, the Ford V8 was shorter, so this was chosen as the preferred motor.

Armament

At the time of the instigation of the TOG Amphibian programme in July 1940, the primary British tank gun was still the 2 pounder. A gun of 40 mm calibre, the 2 pounder was an excellent weapon capable of knocking holes very effectively through the armor of even the heaviest German tanks of the day. It was, however, seen by General Pope as having had its day. There was another gun on the drawing board for tanks and that was a 6 pounder gun. Not the low velocity 6 pounder of WW1 era tanks, but a new gun firing an armor piercing capped (APC) round as well as a usefully large high-explosive round. The old 2 pounder did have a high-explosive shell for it but it saw little service due to the very small charge it carried.

The Army, however, at this time, had at best an ambivalence towards this new gun, due in no small part no doubt to the lack of any tank able to carry it at the time.

The only design, in fact, for which the 6 pounder had even been tried on by this time was the A.12 and that project had ended that month, leaving Sir Albert Stern and the SVDC as the only people interested in it.

Sir Albert Stern was pressing the case hard at this time for adoption of the 6 pounder, in part for TOG-2 but also because he, like General Pope, clearly saw the need for a bigger gun than the 2 pounder for tanks. When Mr. Burton approached him that month then, it would have been no surprise at all if the 6 pounder formed the basis of the armament for both the airborne and amphibian designs the S.V.D.C. considered. Other than a note of the gun for the airborne vehicle, however, it was not to be. General Pope’s requirements were clear and called for a 2 pounder gun instead, and a 2 pounder gun it would have to be.

The gun had been chosen for them but the turret and diameter had not. Stern proposed the adoption of a turret with a diameter of 4’ 6” (54” / 1,372 mm), which would be armored to match the hull, producing a turret around 3.75 tons (3.81 tonnes) in weight when fully armed. This turret ring was slightly smaller than that used on the A.12 Matilda (54.3” / 1,379 mm) and A.22 (54.25” / 1,378 mm) but was exactly the same size as the turret diameter for the Cruiser Mk.III and IV (A.13). This is suggestive that it was to be an A.13 turret which would have been used, although it would have to have been uparmored to meet the frontal armor requirement.

Conclusion

When the N.L.E. did finally finish their own amphibian tank designs in December 1940, they were nothing like the design from the S.V.D.C. Gone was any notion of being underwater. The N.L.E. machines would float. The N.L.E. continued to use the expertise of Mr. Ricardo even after 10th September 1940 and he revealed his views of their alternatives that October. In his report, Mr. Ricardo still emphasized the importance of a secret and safe underwater approach, still pushed for the S.V.D.C. design, and bemoaned the idea of a small floating tank. If a floating assault tank was to be used it should, he argued, be substantially larger and better armed. Mr. Ricardo felt that Mr. Hopkins made far too much of the water-elements of an amphibian tank considering it was only going to be in the water for a few minutes. Further, Mr. Ricardo set-aside much of Mr. Hopkins’ objections especially when it came to the engine stalling underwater and he was on good ground to do so – Mr. Ricardo had, after all, extensive experience dealing with engines for submarines. The result was that no S.V.D.C. Amphibian tank was ever built and for that matter, the British never fielded a dedicated amphibious tank at all during the war.

David Bocquelet’s possible rendition of the TOG amphibian

TOG Amphibian Specifications
Dimensions (LxWxH)	18’ 9” (5.7 m) x 7’ 9” (2.4 m) x 4’ 3” (1.3 m), ground clearance 15” (0.38 m)
Total weight, battle ready	14 tons (14.2 tonnes) (plus or minus 10 %) (12.6 to 15.4 tons / 12.8 to 15.6 tonnes)
Crew	3, commander, gunner, and driver
Propulsion	Ford V8 90 hp petrol or Vauxhall 90 hp petrol
Speed	8 – 10 mph (12.9 – 16.1 km) on land cross country and negotiate water (either above or below the waves) at 4 knots (7.4 kph)
Range (road)	50 miles (80.5 km)
Trench Crossing	5’ 6” (1.7 m)
Step	3’(0.9 m)
Armament	2 pounder gun and 7.92 mm Besa in turret
Armor	Proof against any small arms AP fire at any range. Proof against 37 mm AT fire at 300 yards (ideal) at 90 degrees. Front: 2 ½” (63.5 mm) thick, if needs be down to 2” (50.8 mm) thick where normal shell impact was unlikely. Sides: ⅞” (22.2 mm) thick Floor and roof: 3’8” to ½” (9.5 to 12.7 mm) thick
Radio	No.11 wireless set (or equivalent) as well as an inter-troop radio set

Sources

Hills, A. (2017). The Tanks of TOG: The work, design and tanks of the special Vehicle Development Committee 1939-1945. FWD Publishing, USA
Hills, A. (~2021). Striding Ashore. The History of British Tank and Armoured Fighting Vehicle Amphibious Wading Development in World War II. FWD Publishing, USA
Letter from Sir Albert Stern to Mr. Burton, dated 9th August 1940
Report of Interview between Sir Albert Stern and Herbert Morrison, dated 3rd September 1940
Notes made by Chairman; Visit to Lincoln 14th and 15th August, by Sir Albert Stern
Letter from G. D. Burton to Sir Albert Stern, dated 12th August 1940
Secret note entitled ‘Amphibious Tank Operations’ 1A, undated
Recommendation from Sir Albert Stern for an Amphibious Tank, dated 19th August 1940
Memorandum by Mr. Ricardo on the subject of the ‘Amphibious Tank,’ dated 21st October 1940
War Office Training Film: The D.D. Amphibious Tank: Sherman III D.D., Mark II