WW2 British Prototypes WW2 Canadian Prototypes

OQF 3.7″ AA on Ram Mounting

Dominion of Canada/United Kingdom (1942)
Self-Propelled Anti-Aircraft/Anti-Tank Gun – 1 Built

A joint venture between Canada and Great Britain, the Tank, Cruiser, Ram, was an expedient means of creating a conventionally turreted tank on the bones of the American Medium Tank M3 Lee/Grant. In 1941, the long-term replacement for the M3 was still in development as the T6, later to become the famous Medium Tank M4 Sherman. The Ram would take the American suspension and drivetrain, a new cast hull of Canadian design, and be armed with the British 6-pounder (57 mm) gun in a new turret.

With the Ram approved for service, much consideration was given to the possibility of producing variants based on the new vehicle. The seemingly unending quest for firepower led to these considerations. In 1941, General Frederick ‘Frank’ Worthington, founder of the Canadian Armoured Corps, proposed that a joint self-propelled (SP) anti-tank and anti-aircraft vehicle could be built on the Ram’s chassis, mounting the powerful British Ordnance Quick-Firing Mk.II 3.7-inch (94 mm) heavy anti-aircraft gun. In 1942, the Canadian Army Over-Seas (CAOS) requested that this proposed design undergo further development, alongside a proposed self-propelled artillery piece that would become the Sexton.

What would emerge from this is the ‘OQF 3.7″ AA on Ram Mounting’. However, one of the first obstacles to overcome is just what this thing was called, as it would appear it never received an official designator. Both official papers from the time and post-war literature list multiple variants. The chosen designator used as the title of this article is simply one of a litany of names. These include, among others – ‘QF 3.7” AA SP on Ram II Chassis’, ‘OQF 3.7” Ram’, ‘3.7 Ram’, ‘3.7” SP’, ‘3.7” SP Gun Carriage’, and ‘3.7” AA on Ram Mounting’.

The Canadian OQF 3.7” AA on Ram Mounting, based on the domestically produced Ram Cruiser Tank. The SP was also known as ‘QF 3.7” AA SP on Ram II Chassis’, ‘OQF 3.7” Ram’, ‘3.7 Ram’, ‘3.7” SP’, ‘3.7” SP Gun Carriage’, and ‘3.7” AA on Ram Mounting’.

Tank, Cruiser, Ram

With its sponson mounted main armament and secondary turret, the Medium Tank M3 Lee, and its British version, the Grant, was only ever seen as a stopgap solution to getting a more capable tank into the hands of the British Army in North Africa. Its more desirable replacement, later to become the famous M4 Sherman, was still in development, and it would take some time before it was ready for combat.

Rather than wait on this, the British Tank Mission in the US and the Canadian General Staff took it upon themselves to design a new tank based on the M3’s hull. This tank would be built in Canada, and intended to be used by both the Canadian and British Armies. What would emerge was the Tank, Cruiser, Ram, also known as the Sherman VI in some British documentation and as the M4A5 in the US. There were two models, the Ram I and Ram II, with the main difference being the armament. The Ram I was armed with a 2-pounder/40 mm gun from the Valentine Infantry Tank (also being built in Canada at the time), whilst the Ram II was armed with the larger, more powerful 6-pounder/57 mm gun.

Mid to late model Ram II at the Tank Museum, Bovington, UK. Photo: Author’s Own

The Ram featured a new fully cast hull with the main armament located conventionally in a fully rotating turret. As stated previously, this would be a 2-pounder or 6-pounder depending on the model. Secondary armament consisted of three .30 Cal. (7.62 mm) Browning M1919 machine guns. One was mounted coaxially to the main gun, and another was placed in a sub-turret at the front left corner of the hull (akin to early models of the British Crusader), with the third being pintle mounted to the commander’s hatch.

With the automotives, the Ram shared much with the M3 Lee. The engine, drivetrain, transmission, suspension, and tracks were all the type found on the American tank. The engine consisted of the large, 400 hp Continental R-975 9-cylinder radial gasoline engine, which propelled the 28 ½ ton (29 tonnes) tank to a top speed of 25 mph (40 km/h) via a forward sprocket wheel. The weight of the vehicle was supported on the typical Vertical Volute Spring Suspension (VVSS) with three bogies per side.

Built at the Montreal Locomotive Works (MLW), 1,899 Rams were produced, with the last one rolling off the production line in 1943. As a gun tank, the Ram would never see active combat, but it did prove to be a valuable training tool for Canadian tankers, who used them in both Canada and the UK. Variants of the Ram did see service in the War, however. These were the Ram Kangaroo, an ad hoc Armored Personnel Carrier (APC), the Ram Command and Observation Post (COP) vehicle, and the Ram ‘Badger’, a turretless Ram equipped with a flame thrower.

A Ram Kangaroo APC in operation, North West Europe, 1945. Photo: The Tank Museum, Bovington

Bringing Bam to the Ram

CAOS’ request of May 1942 was for the development of a high-velocity, long-range, and highly mobile anti-tank gun. The Director of Artillery (DArty) formulated two proposals from this request, which he then passed to the Army Technical Development Board (ATDB). The first proposal, and clearly the easiest method of achieving the goal of CAOS’ request, was the adoption of the American T35 tank destroyer, which would later enter service as the 3in Gun Motor Carriage M10 Wolverine. The more radical proposal was to take a Canadian-built chassis, and place upon it the most powerful gun available in Canada at that time, the Ordnance Quick-Firing (OQF) 3.7-inch (94 mm) heavy anti-aircraft gun.

The Ordnance Quick-Firing (OQF) 3.7-inch (94 mm) Heavy Anti-Aircraft Gun was the go-to anti-aircraft gun for British and Commonwealth forces during the Second World War. Developed in 1937, the gun was produced under license in Canada by the General Electric Company ‘Genelco’. It was a large weapon, at 9 tons (9.3 tonnes), and powerful, able to propel a shell to a ceiling of up to 25,000 ft (7,600 m) at an initial velocity of nearly 2,700 fps (823 m/s) with an elevation range of +85º to -9º.

On its towed mount, the gun was used in almost every theater of war, barring the Eastern Front, and played a key role in defending London during the Blitz. The 3.7 was only ever equipped with high-explosive (HE) and shrapnel shells. Nonetheless, there are accounts from both the North African and Burmese campaigns, describing that the guns were leveled at attacking tank units numerous times, scoring multiple kills respectively. Had the 3.7-in SP entered full production and service, then perhaps a dedicated anti-tank round would have been developed. That being said, a comparative table drawn up in May 1943 by the artillery branch lists penetration of the 3.7-inch as “98.2 mm @ 30-degrees”. Unfortunately, it does not list the distance or shell type that made this 3.8 inch hole.

The OQF 3.7-in gun on its usual towed mount in Hyde Park, London, 1939. Photo: IWM

Much like the Sexton Self-Propelled Gun, initial thought was given to placing this gun on the chassis of Canadian-built Valentines. This idea was quickly abandoned in favor of the Ram chassis, as it was a much sturdier base for the heavy 3.7-inch gun. After reviews of the proposal by DArty, the concept evolved into that of a self-propelled heavy anti-aircraft gun that could also perform the role of a self-propelled anti-tank gun. On July 23rd, 1942, following another review by the Army Engineering Design Branch (AEDB), the ATDB approved the construction of a single prototype designated ‘Project 14A’. There was also a ‘Project 14B’, a similar concept to the 3.7-in mounting, but with a 40 mm Bofors anti-aircraft gun instead. This was abandoned, as the US were working on similar projects. With construction approved, the project advanced at pace.

Ram on the Range

In just 9 ½ hours, MLW (initial builders of the Ram tank) were able to modify an existing chassis by removing almost everything from the upper hull, leaving just the automotive bearing lower half, and relocating the fuel tanks. It is pretty safe assume that the driver’s position, controls and instruments remained unchanged. On July 27th, 1942, this stripped-down hull was shipped to Genelco’s plant in Ontario. The gun, specifically a Mk.II gun on a Mk.III mounting, was stripped of everything that sat below the 52 inch/132 cm diameter ‘turret’ ring (wheeled carriage, lead predictor, etc) and placed onto the stripped Ram chassis. This completed vehicle was then sent to the Artillery School in Petawawa, Southern Ontario, where firing trials were carried out between August 27th and September 2nd.

Early ‘proof of concept’ of the 3.7-inch (94 mm) gun on the stripped down hull of a Ram, designated ‘Project 14A’. The vehicle is seen here during the Petawawa firing trails. Photo: r/TankPorn & Service Publications respectively

The results of the gunnery trials were promising. Its performance in both direct and indirect fire tests were considered excellent, although a dedicated direct-fire sight was much desired. As well as the sight, some improvements would need to be made before the project went any further. The weapon’s rate of fire was hampered by the limited space available on the vehicle, and inserting a shell into the breach became more difficult with any increase in elevation. Perhaps the biggest problem was the effect of recoil. Firing of the gun caused the vehicle to rock quite violently along the line of fire. If the gun was facing forward, it was found the parking brake was not sufficient to hold the vehicle in place and would slide on slick surfaces. Firing at any degree on the horizontal plane would cause the vehicle to tilt rather drastically. It was hoped that strengthening the volute springs of the suspension units would amend this, as at this point, they refused to re-settle back to their pre-fire positions. All of this made it impossible for the gunner to hold zero, which again hindered the rate of fire. This tilting would also need to be rectified if the vehicle was going to discharge any form of accurate and sustained predictor-led anti-aircraft fire. As a remedy, an improved hand brake was recommended, and there was even some consideration given to lengthening the hull.

Ramping it Up

After the initial trials, the Ram was sent back to Genelco’s plant in Ontario. There, it would be fitted with a wooden mock-up of the planned armor layout. This consisted of a large, flat gun-shield with curved edges, and simple flat boards along the flanks and front of the hull that could fold down to form a larger firing platform. Apertures were cut into the front board to allow vision for the driver and co-driver. It was planned that a simple hatch for the driver would be installed at a later date. The addition of the folding platform answered the problem of limited working space. Once this wooden shell was installed, the vehicle also returned to MLW, where several improvements were made to the hardware.

The Ram SP at the General Electric Company’s plant in Ontario with the temporary wooden ‘armor’ installed. Photo: r/TankPorn

The Montreal Locomotive Works effectively ‘finished’ the modified Ram. Working off of Genelco’s wooden template, they installed a mild-steel shell to the vehicle. If the vehicle had entered production, this would of course have been replaced with hardened armored steel. Even so, this shielding was only ¾ inch (19 mm) thick, just enough to protect the crew from shell fragmentation. In addition, stowage for a total of 40 rounds were installed over each track, and a special box was installed at the rearmost edge of the deck for a No. 19 wireless set and accompanying intercom system. Leveling bubbles were installed to make sure the vehicle did not stop on a gradient of more than 3º, the maximum inclination the gun-carriage could be cross-leveled on. New elevation and traverse gear designed by Genelco were also installed to allow accurate low angle fire. Backup gun control handwheels, and the standard issue No. 9 dial sight were added for indirect fire. Most importantly, seats were added for the crew.

With this work complete, final crew arrangements were made, and mass and dimension measurements were recorded. The exact number of crew differs between source material. Some literature describes a crew of 11, while official documents are anything from 7 to 9. As only one piece of official paperwork (a letter from Lieutenant-Colonel E. W. Archibald dated 1943) lists the positions and roles, this shall be used further. At least 9 crew members would operate the vehicle, consisting of the commander, gun layer (elevation), gun layer (bearing), loader, fuze setter, driver, and radio operator. The driver and another crew member (which one is unknown) were located in the hull, while the rest of the crew were located on the gun deck. The modified Ram weighed in at 28 ½ tons (29 tonnes), a ton (around a tonne) lighter than the regular gun tank. The addition of the 3.7-inch gun increased the total length of the vehicle to 20 feet (6.1 m) and increased the height to 10 foot 9 inches (3.3 m). The width went the opposite direction, being 10 inches (25 cm) narrower at 9 feet (2.75 m).

The Ram 3.7in SP in what would be its final form, with mild-steel shielding. Photos: Profile Publications/Service Publications

The vehicle underwent further firing and road running tests at Petawawa, before being sent to Halifax, Nova Scotia for anti-aircraft gunnery trials. On October 10th, 1942, the vehicle was tested against a target drogue – an aerial target towed by a separate aircraft. Compared to the ground-target firing, the results of the anti-aircraft tests were less optimistic. A number of final additions were also made to the vehicle while in Halifax. This included a travel-lock for the gun, a sliding driver’s hatch, and new mud guards. These were fabricated by the Clark Ruse aircraft plant. New gunnery sights were also installed, consisting of two No. 33 scopes. During the trials, a new No. 42 7×50 anti-tank scope was also tested, but was found to give no real improvement over the No. 33.

Ramming it Home

On November 13th, 1942, the Ram SP AA was shipped to Great Britain. Upon arrival, it was sent to the Canadian Base Ordnance Depot (CBOD) at Bordon in Hampshire where, in December, it would receive the catalog number ‘CT43615’. Further improvements would be made to the vehicle, particularly the traverse gear, before being sent to the Larkhill Artillery Range. Operated by men of the 2nd Heavy Anti-Aircraft Regiment, Royal Canadian Artillery (RCA), the Ram SP underwent further live fire trials, this time alongside the prototype Sexton, from December 1942 to January 1943.

The Ram SP on trial. The Canadian Army numbering on the side suggests this photo was taken before the prototype came to the UK. Photo: Profile Publications

Despite performing well in the trials, the British top-brass could not see a need for the vehicle as a whole, other than as a support weapon during combined forces operations to provide either air or land cover fire. It was felt that in this role, it would be useful for amphibious landings, initially used offensively against ground targets, then switching to a defensive roll at a beachhead. Therefore, arrangements were made for it to take part in the planned beach landing trials in February 1943. The cross-leveling issue continued to dog the gun mount. The 3º limit was undesirable and it was requested that Genelco back in Canada look into an improved mount that could be developed without drastic and time-consuming modification. Genelco’s response was not optimistic, stating that it would take at least a year to design, build and test any new gun mount.

On January 17th, 1943, the Ram SP was sent to the Anti-Aircraft School at RAF Manorbier, Lydstep, South Wales, where further problems with the arrangement of the gun and platform became apparent. The coastal area of RAF Manorbier consists mostly of grass-covered rock, and it was found that the vehicle was extremely unstable on such terrain when firing.

Depending on the degree of horizontal traverse, the gun-shield often collided with the platform, especially if it was on uneven ground. Due to this, it was recommended that horizontal traverse be limited to 90º to either side. The platform was also found to be far too small, with a high risk that a crew member would fall off. Operation of the weapon came with its own problems. Loading required a dismounted member of the crew to unload rounds from the stowage rack, and pass them up above shoulder height to a waiting loader, not easy when the 3.7-in shells could weigh up to 50 lbs (23 kg). The loader had it no easier, loading the gun at any elevation under +50º was relatively easy, but as soon as the gun elevated past this, the task became harder. With each notch higher, the loader would have to fight gravity to push the shell up into an almost vertical breach.

A couple more issues were highlighted with the firing of the gun, one being the continued issue of the gun not returning to the same point of aim post-discharge, making a quick follow up shot impossible, as the gunner would have to re-aim the gun. A second, more dangerous quirk, to the operators at least, was the empty propellant case that would automatically be ejected from the breech. Depending on elevation and degree of traverse, the case would smack into the radio box at the back of the platform, damaging the radio set, but also posing a risk of hitting a crew member. Getting smacked in the face with a hefty brass case was not considered ideal.

The Ram 3.7in SP during trials at RAF Manorbier, South Wales in 1943. The shielding has been folded down to allow the gun to traverse freely. Photo: Service Publications

Rambunctious Ram

Following this series of extensive gunnery trials, and with the highlighted flaws, it was suggested that the Ram SP not be accepted for service unless drastic improvements were made to the design. Among other things, suggested improvements included raising the gun mount to remedy the gun-shield colliding with the rest of the deck, widening the folding platform sides to 3 feet (90 cm), developing/installing an automatic loading system, and an improvement to crew comfort in the form of padded seating.

After the January 1943 anti-aircraft trials, personnel of the 1st Canadian Artillery Brigade compiled a report of their own, effectively a user review of the vehicle. They found that the weapon system was fast and easy to bring to action, its height was beneficial to firing over cover, was an effective provider of anti-armor and anti-fortification fire support, and, it was able to traverse terrain a normal towed artillery piece could not. On the other hand, the crew were somewhat vulnerable behind the relatively thin shielding from both enemy fire and the elements, its height presented a noticeable silhouette, and it would require back-up from tracked support vehicles. All very well if the gun could get into a position if its supply train could not.

Another view of the vehicle at RAF Manorbier in 1943. This shows how little room there was on the vehicle for the entire gun team. Note the loader attempting to shove a 50 lb (23 kg) 3.7” shell into the near vertical breach. Photo: Service Publications

Ram in the Waves

In late January, both the 3.7” Ram and the prototype Sexton would be sent to Poole, Dorset to undergo waterproofing for amphibious assault exercises that were held there, but also at Instow, North Devon, by the Combined Operations Experimental Establishment (COXE). They would conduct various means of beach entry, whether via direct beach landing or wading in. For the wading, extended air-intakes were added to the engine bay.

Live fire trials were also held at Poole, with 3.7” discharge from both a floating Landing Craft, Tank (LCT) and a beached LCT. The floating firing platform raised serious safety concerns, not least because the range at Poole was only 3,000 yards (2,700 m) long, and any wave at an inopportune moment could send a shell flying well over the range, something that happened numerous times. Whether these errant shells hit anything is unknown. Nonetheless, the Ram SP proved once again to be an effective, fast-firing, and highly accurate platform in a direct fire capacity. However, firing from a floating platform posed more problems. As it would be expected that, once its fire mission was complete, the vehicle would wade onto the beach, the shielding was kept in the travel position, limiting both the traverse of the gun and the amount of space the crew had to work in. Second to this, the recoil force and over-pressure from the gun fire caused several of the waterproof seals to rupture.

The 3.7” Ram SP on board Mk.5 LCT ‘No. 2307’ during the COXE trials. Note the wading ‘snorkel’ attached to the rear of the engine bay. Photos: National Museum of the Royal Navy, via The D-Day Story

In an indirect-fire artillery support function, the test results were less favorable. Firing afloat was impossible due to the instability of the platform. The No. 9 dial sight could not be used on an uneven sloping beach, leaving the gun-layer to ‘go old-school’ and use a range-clinometer. And so began the final downfall of the 3.7” Ram project.

Ram Bam Thank You Ma’am

In 1943, Major W. H. Carr, Technical Liaison Officer, Artillery, of the Canadian Military Headquarters (CMHQ) in London concluded that everything the 3.7” gun could do, the newly developed 17-Pounder could probably do, if not better. He had even suggested, and drawn up his own report, on a proposal to form an ad hoc self-propelled anti-tank gun by installing the 17-pounder on the Sexton, which, unlike the 3.7”, had just entered service with Canadian and British artillery units. However, this proposal was never acted on.

The 3.7” Ram on the beach during the COXE trials. Photo: National Museum of the Royal Navy, via The D-Day Story

The final nail in the coffin came on June 23rd, 1943, when the Army Technical Development Board (ATDB) terminated ‘Project 14A’. In August, the vehicle was broken down. The gun was restored to a standard 3.7” towed gun, while the hull was returned to Canadian Base Ordnance Depot (CBOD) at Bordon, where it was used as a towing vehicle. Consideration was given to creating an improved version of the vehicle that would perform more of an ‘assault gun’ role with thicker armor and an enclosed fighting compartment, although this was officially dismissed by October 1943.

While the 3.7” Ram project ultimately failed, it proved that the Canadian Military were quite capable of producing their own effective armored vehicles, and did not have to rely on either Great Britain or the United States to create such equipment. Canadian arms manufacturing would continue throughout the course of the war, and while production of the Ram II gun tank would cease in 1943, Montreal Locomotive Works would continue to build tanks. With the Ram gone, MLW began to produce the ‘Grizzly’, a license-built Canadian version of the American Medium Tank M4A1. A Self-Propelled Anti-Aircraft Gun (SPAAG) project would also spawn from this, namely the quad 20 mm gun-armed ‘Skink’.

Tank AA, 20mm Quad, Skink, a Canadian-design AA vehicle based on a Canadian-built tank. Photo: Wikimedia

The Canadian OQF 3.7” AA on Ram Mounting, based on the domestically produced Ram Cruiser Tank. The SP was also known as ‘QF 3.7” AA SP on Ram II Chassis’, ‘OQF 3.7” Ram’, ‘3.7 Ram’, ‘3.7” SP’, ‘3.7” SP Gun Carriage’, and ‘3.7” AA on Ram Mounting’. In this view, the crew platform’s shielding is in the raised position.
The OQF 3.7″ Ram with the gun elevated. The range of elevation was -9º to +85º. When in firing mode, the shielding of the crew platform folded down allowing the gun to traverse and the crew to move around. Both illustrations by Oussama Mohamed ‘Godzilla’


Dimensions L-W-H 20 ft x 10 ft 9 in x 9 ft (6.1 x 3.3 x 2.75 m)
Weight 28 ½ tons (29 tonnes)
Crew ~9 (commander, gun layer (elevation), gun layer (bearing), loader, fuze setter, driver, and radio operator)
Propulsion Continental R-975 9-cyl radial petrol/gasoline, 400 hp (298 kW)
Speed 25 mph (40 km/h)
Suspension Vertical Volute Springs (VVSS)
Armament Ordnance Quick-Firing (OQF) 3.7-inch (94 mm) Heavy Anti-Aircraft Gun
Armor ¾ inch (19 mm) Shielding
Built 1


Project 14A, Brief Specifications of 3.7” AA SP on Ram II Chassis, Official Paper, 1942-43

Chris Ellis, Peter Chamberlain, AFV Weapons Profiles, No. 13: Ram and Sexton, Profile Publications, 1970

John F. Wallace, Dragons of Steel: Canadian Armour in Two World Wars, The General Store Publishing House, 1995

Graham Broad, “Not competent to produce tanks” The Ram and Tank Production in Canada, 1939-1945, Canadian Military History Volume 11 Number 1, Beacon Herald Fine Printing Division, 2002

Paul Roberts, The Ram – Developments and Variants, Vol. 1, Service Publications, 2002

Paul Roberts, The Ram – Developments and Variants, Vol. 2, Service Publications, 2004

Roger V. Lucy, Canada’s Pride: The Ram Tank and its Variants, Service Publications, 2014

The D-Day Story, Instow Photographic Collection, Portsmouth, UK

Canadiana Héritage, Department of National Defence Subject Files 1866-1950: C-8386 (LINK)

Canadiana Héritage, Canadian Military Headquarters, London: C-5794 (LINK)

By Mark Nash

X: @mr_m_nash.
120 articles & counting...

2 replies on “OQF 3.7″ AA on Ram Mounting”

Great article!

Just a nitpick- “Variants of the Ram did see service in the War, however. These were the Ram Kangaroo, an ad hoc Armored Personnel Carrier (APC), and the Ram Command and Observation Post (COP) vehicle.”
There was actually a third variant of the Ram used in combat- the Ram Flamethrower, sometimes referred to as either the Badger or Cougar in Canadian period documents.

I thought I missed one. It has been added to the Honorable Mentions, Thank you.

– Author | TE Staff

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