Monday, 13 March 2023

Anti-Aircraft Lizard

The British began to build SPAAGs after the start of the Second World War. As soon as it became clear that the Light Tank Mk.VI was obsolete as a tank, it was converted to take a new turret with four AA machine guns. The same thing was done to the Crusader tank, but with two 20 mm Oerlikon autocannons. This armament upgrade did not resolve other issues with these tanks, namely thin armour and poor reliability. Finding spare parts for these out of production vehicles was not the easiest task either. It was clear that a SPAAG based on a chassis still in production was needed. Since Canada was just setting up production of the Grizzly tank, a variant of the American Sherman, this vehicle was chosen as the chassis. This was the start of the Skink AA tank, which was built and even saw battle, unlike the tank that it was based on.

Born to crawl

Work on mechanizing the 20 mm AA gun began in December of 1942. The AFV Users Committee suggested building an AA tank on the chassis of either Ram or Sherman tank for escorting armoured units on December 19th. The committee required the vehicle to be equipped with either two or four 20 mm guns, carry 600 rounds of ammunition, and be able to fire at targets moving at a speed of up to 350 mph (563 kph) at a height of 100 yards (91 meters). This required the turret to rotate a full 360 degrees in 4.8 seconds. The vehicle’s armour was required to withstand a hit from a 40 mm aircraft cannon at a range of 100 yards.

Development of this new vehicle began on March 19th, 1943. The initial variant called for a new turret welded together from 25-50 mm thick armour plates. The turret contained a quad Hispano-Suiza gun mount. Each gun was fed with a 50 round belt. The mount could be aimed vertically at a speed of 45 degrees per second and horizontally at a speed of 55 degrees per second. Production of such a vehicle was pitched to the Angus Shops and Montreal Locomotive works as well as the American General Motors company, but all three declined this project.

Skink AA tank with an early cast turret. This tank still has Hispano-Suiza guns.

The military had to work on the vehicle themselves. The Army Technical Development Board (ATDB) developed the turret and passed the blueprints on to the Waterloo Manufacturing Company for the production of a full sized model. The ATDB presented this model on September 18th and received permission to produce two welded turrets. A turret was tested on its own on December 11th and on a tank chassis on January 14th, 1944.

The turret passed trials, but due to its complex shape welding was not the optimal solution. A cast turret with 57 mm front armour, 50 mm sides, and 25 mm roof and rear was ordered at the Dominion Foundries of Hamilton. With armament, this turret weighed 3400 kg, and a fully stowed vehicle with this turret would weigh 28.6 tons. The vehicle was named Skink after the only kind of lizard to live in Ontario to highlight the fact that this tank did not originate in Quebec. Incidentally, the Skink was always referred to as an anti-aircraft tank, never as a SPAAG.

The turret held three crewmen. The radio operator and commander (who also served as the loaders) were placed along the sides. The gunner sat in the middle. The traverse mechanism was the same Oilgear type used on the Grizzly tank, but modified to allow for the required traverse speeds. The generator powering the traverse motor was also changed to supply 70 A current instead of 50 A.

Gun elevation and turret traverse were controlled by joysticks. The left and right pair of guns were fired with a trigger button on the corresponding joystick. The electric firing mechanism used Magnavox solenoids. Each gun had its own trunnions and mantlet. The guns were aimed using a modified Mark IX naval sight with the ability to introduce corrections from the Teleflex antiaircraft detector.

Quad Polsten gun mount, Irish Military War Museum. The Skink was modified to use these guns instead of the Hispano-Suiza.

Since the turret was compatible with the standard Sherman turret ring, it was easy to install on an existing chassis. Development was going well, and so the Canadian army ordered 300 turrets for their own needs and the needs of the British, who also showed interest in this project. The British had a harder time with these vehicles, as it turned out that they had neither the spare chassis nor technicians available to perform the conversion. The British tried to obtain additional tanks in the US and have them converted in Canada on December 21st, but nothing came out of it.

Rearmament by necessity

A plan approved on January 21st, 1944, called for the arrival of the first Skinks in the UK in May or June, but the order was altered on March 8th. Now only 135 Skinks for Canada and 130 turrets for the British were planned. Another serious hit to the project was delivered soon after. The 21st Army Group decided to stop using the Hispano-Suiza gun as it was easier to obtain ammunition for the Oerlikon. The Skink had to be converted to take the Polsten gun, a simplified variant of the Oerlikon produced in Canada.

20 mm Polsten gun with mounting.

The turret with new guns was tested at the factory from May 5th to May 22nd, 1944. It turned out that the change in armament would be a difficult journey. The turret was too small to work with 60 round magazines, so 30 round magazines had to be used. Even with this limitation, the two upper Polstens had to be turned by 40 degrees so that the magazine fit into the turret.

Installation of the left pair of Polstens in the Skink’s turret.

The vehicle could carry 60 magazines in addition to the four loaded into the guns. There was enough room on the floor of the fighting compartment for 12 empty magazines, so it was not necessary to throw them out of the turret as soon as the guns were reloaded. This was unsatisfactory for the British, who insisted that 200 round belts must be used. The Polstens also jammed often when using Canadian ammunition, although British and American ammunition worked flawlessly. Trials also showed that in still weather the smoke generated by the guns hung around and impeded aiming. Just over 1% hits were scored against a target balloon moving at 193 kph.

There was another drawback. When firing, the gunner had to open his hatch and stick his head out of the turret, rendering him vulnerable to shell splinters or bullets ricocheting off the sloped turret front. The tank was generally very raw and had a lot of defects to resolve. Nevertheless, American observers present at the trials held on May 19-20th commented that the tank was superior to any analogous American vehicle.

Drawing of the Skink’s turret and turret basket made by an American observer.

The British “belt lobby” was influential enough that work on a belt feed for Polsten guns began early in 1944. The solution was quite poor compared to the American feed. While the Hispano-Suiza could take a belt from either the left or the right, the mechanism developed for the Canadian gun by the Molins company could only feed from the left. This was a big problem for the quad mounting.

Trials held in January of 1944 showed that the Skink turret would have to be altered to accept belt fed Polsten guns, which was unacceptable. Some components were also taken from the Hispano-Suiza and thus only worked with 50 round belts. The only saving grace for the Skink at this point was that a successful belt feed could not be developed for the Crusader AA or Centaur AA either, although many documents on development of belt feeds for these vehicles were also sent to the Canadians. Regardless, development of a belt feed for the Polsten was cancelled on July 7th, 1944, when it was clear that the project hit a dead end.

The start of production was planned for September of 1944, but there was a new complication. The 21st Army Group noticed the rapid decrease in the effectiveness of the Luftwaffe back in July. All orders for SPAAGs and AA tanks were cancelled. Only three Skinks and 8 turret kits were finished.

Trials with no production

Even though the Skink was not going to be mass produced, the concept was considered to be promising. A decision was made to put the tanks that were already built to the test in order to discover drawbacks that could be corrected in future generations of these vehicles.

One turret was sent to Valcartier, Quebec, for splash trials. On October 28th, 1944, it was installed on a Grizzly chassis and tested. Trials showed that splash protection was insufficient, as it was possible to wound the gunner with splash from rifle bullets that passed through his open hatch. Significant amounts of splash also entered the turret through gaps around the gun mantlets.

Skink armed with Polsten guns.

A Skink tank with serial number 1001 arrived in the UK in September of 1944. A second sample was to be sent in March of 1945, but the British changed their minds, reasoning that it was better for one vehicle to remain in each country so that the bill may be split evenly. There was also a proposal to keep the second tank in exchange for cancelling the order for three turrets, but it seems that neither the turrets nor the second tank ever made it to the UK after all.

The experimental Skink arrived in Chobham in early October where it was tested at the AA gun laboratory at the Department of Tank Design. These trials were finished by the end of October. The officers present for the trials were satisfied with the Skink’s performance. They considered it to be superior to existing SPAAGs and AA tanks. The traverse mechanism was superior to the one used on the Centaur AA. The report author noted that the vehicle was not living up to claimed performance. Maximum traverse speed measured in Canada was 62 degrees per second, but the British measured only 48 degrees.

The Skink arrived at the artillery proving grounds at Lulworth on October 25th, 1944. Inspection showed that some stowage items had been lost. The hydraulic system compressor motor also had to be replaced. Trials began on November 15th, but priority was low, so they were only finished in January of 1945. Aiming trials at targets moving at speeds of 480, 640, and 966 kph at a range of 320 meters showed that it was difficult to follow a target due to an uneven rate of acceleration, but testers judged that one could get used to this. A more serious limitation was the jerky behaviour of the turret at low traverse speeds. The testers considered that changing the traverse gear ratios could solve this issue, but it would require a reduction of the maximum traverse speed to 50 degrees per second.

Drawing of the Skink from a conversion manual. Not a single vehicle was ever converted outside of Canada.

The guns were balanced precisely. If the magazines were full and the bolts were pulled back, the guns were breech heavy. With partially full magazines and the bolts forward, the guns were muzzle heavy. Since the elevation mechanism had no issue with a small imbalance, the testers suggested moving the guns backwards slightly to prevent vibration during firing.

The electric system worked well. No defects were found during the trials. Starting the engine was difficult in the cold, and so the batteries died quickly, but they could be fully recharged in less than half an hour. The main generator worked flawlessly. The auxiliary generator also worked well, with the exception of one case where water got into the fuel. The hydraulics worked poorly. Disassembly and inspection showed no obvious cause, but the mechanisms began working better once reassembled.

As was already established in Canada, the vehicle was vulnerable to small arms fire. There was a 2.5 mm gap under each Polsten gun that could let in splash. Splash could also enter through the gap between the barrel and gun mantlet.

The sight mount was considered unsatisfactory. The sight was wobbly and shook when the gun was fired. Since the Canadians did not lubricate it properly, the adjustment screw rusted in place. The testers suggested that the right half of the mount should be removed, as it blocked the gunner’s view, got in the way of him using his hatch, and also did not do much to help keep the sight in place. The sight itself was also criticized, as it was only suitable for firing on targets moving at a speed of up to 240 kph.

Skink on trials in the UK.

Unlike the other components, the Polsten guns worked badly, giving many misfires during trials. Misfires happened less often if there was more lubricant on the ammunition. The magazines poorly lined up with the opening in the receiver, but one could get over this drawback given sufficient practice. The magazines also worked poorly. Due to improper assembly their lids could open on their own, and one even flew off during trials. The ammunition bin lids also opened on their own, especially when the tank was driving on rough terrain. The travel lock was also deemed inadequate. Rather than a clamp that held the guns at 20 degree elevation, the testers suggested a friction type lock that could let them be fixed at any elevation.

The gun depression and elevation were measured at −4°52’ to +77°34’, slightly less than nominal due to the gun mantlet catching on the turret. The guns covered up the safety when depressed. When the guns were elevated rapidly, the elevation mechanism rammed into the gun mount with such force that the cylinder guide rod bent. This issue had to be corrected using a file. The sight calibration mechanism also had to be filed down, as the acceptable range was not enough to align the guns and the sight. The gun mount had lots of small issues like these, all of which were corrected during the trials.

Despite these issues, the gun mount worked well in practice. Firing on a target balloon resulted in several hits, although the capacity of the magazines only allowed for a single pass. The testers suggested only firing with two guns at a time to save ammunition. This tactic had a problem as firing just one pair of guns turned the turret.

It took 14-17 seconds to reload all guns when ammunition racks on the floor were used. It was much harder to get to the rest of the ammo racks, especially the ones under the turret basket. It was easiest to load the guns at 43 degree elevation. Reloading had to happen often, as 30 rounds were only sufficient for 4.5 seconds of firing. One magazine could be filled by hand in 2 minutes and 40 seconds. Overall, the testers at Lulworth rated the tank very positively. Even though a long list of desired changes was composed, the testers noted that the tank was ready for service as is.

Battle on lizard-back

The single Skink still saw battle. The prototype sent to the UK for trials was passed on to Canadian forces fighting in Europe. The 1st Tank Demonstration Unit composed of Captain Walle, Captain Marshall, Sergeant Bogden, Private Champagne, and Staff Sergeant Major Moore was formed to crew the vehicle. Four new guns were ordered to equip the tank before it was sent off. The tank and its crew arrived in Antwerp on January 24th 1945, and were assigned to the 2nd Canadian Armoured Brigade. The vehicle accompanied various regiments of the brigade from February 6th to March 11th. The Skink returned to the UK on March 25th, 1945.

The turret with its hatches opened. The gunner’s position in front of his hatch made him vulnerable.

The Luftwaffe was on the brink of death by the time the Skink arrived on the mainland, and the crew only spotted an enemy airplane once. It was not possible to engage it, as the crew was outside of the tank and the vehicle was not prepared for battle at the time.

In absence of air targets, the Skink was used against entrenched infantry. The vehicle was sent in as a part of the second echelon under the cover of regular tanks to clear out pockets of resistance left behind after the first echelon. Eyewitnesses describe that a burst of 30 HE-fragmentation-incendiary shells fired over the span of one second were a sight to behold. These shells were very effective at quite literally smoking out enemy infantry that was entrenched deep in structures where it was difficult for ordinary HE to reach them. In one instance, a burst from the Skink convinced 45 Germans to surrender, even though the gunfire only wounded 10 of them. According to Captain Walle, the remaining troops were quite frightened.

The turret with closed hatches. The gunner couldn’t aim in this position, plus splash could enter the turret anyway.

If the enemy was entrenched in brick buildings, the Skink fired at windows. An instance was recorded where a sniper opened fire at the tank’s commander when he peeked out of the turret. Return fire from the Skink in his general direction compelled the sniper and two more soldiers to surrender.

The Skink never engaged enemy tanks as it did not carry AP ammunition. The tank was fired upon by enemy tanks one time. The vehicle retreated, and the enemy tanks were engaged by accompanying Fireflies.

The Canadian tankers liked the Skink, especially the greater protection it offered compared to the Crusader AA and improvised 20 mm SPGs designed to suppress infantry. However, the Skink had its drawbacks. Thickly greased ammunition resulted in jams in dusty conditions. In one case the commander was so busy correcting them that he could not control his vehicle, as a result of which the driver made a wrong turn and ended up in a vulnerable position. It was very difficult to work the bolt on the Polsten by hand. The report from this mission suggested adding a pneumatic or hydraulic assist for racking the bolt.

The Skink is ready for battle. Unlike a regular Grizzly, there are planks welded to the upper front hull.

Due to the original purpose of the vehicle, it was only possible to fire at ground targets at close range, plus protection from ground based threats was not well thought out. If the gunner’s hatch was closed, his sight was unusable. The hatches were also quite small and difficult to use in winter clothing. Additional problems with the magazines were discovered. Their springs quickly wore out and became useless. The report author suggested replacing the magazine feed with a belt feed, citing the flawless function of the Hispano-Suiza guns operated by the 2nd Armoured Brigade.

The Skink’s CDP tracks also gave issues. The track links themselves worked fine over the course of the 800 km trip, but track pins had to be changed often. No other defects were found. CDP tracks were also not compatible with the Extended End Connector, which limited the Skink’s off-road mobility.

As a result of this experience, the 1st Army asked for six Skinks for each regiment, but it was too late. The war was over. Even though the Skink showed itself well, it was not feasible to restart production for such a small order. The only purpose of the tank on the mainland was to gather information for further development of ground based 20 mm autocannons.

One of the surviving Skink turrets. Photo by Clive Prothero.

Trials of the Skink continued after the trip to Europe. The vehicle was brought to the Tank Armament Research facility in Porton by May of 1945 for a thorough study and trials against airborne targets. It remained there until at least July, waiting for equipment from the Royal Air Force to arrive. The tank’s trail ends there. As for Canadian Skinks, all the hulls were scrapped and the turrets were used as range targets. Three of them survived, but still require restoration.

  • Dept. of National Defence / Library and Archives, Canada
  • Canadian Military Headquarters, London (1939-1947) RG 24 C 2
  • Roger V. Lucy. Canada's Pride. The Ram Tank and its Variants — Service, 2014
  • Harold A. Skaarup. Armoured Fighting Vehicles preserved in Manitoba
  • Technical Description of Turret Equipment for Tanks, A/A, 20 MM Quad. SKINK. July 1944
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