Did you know about Australia’s rude tank?

Things are sometimes remembered for all the wrong reasons. One example of this is the Australian AC1 Sentinel tank. It could be remembered for being the only tank every manufactured in quantity in Australia; for being the first tank ever to feature a single-piece cast hull; or as a triumph of dedication and ingenuity in a country which had no tank design experience and practically no heavy industry. Instead, it’s remembered for… something far less lofty. 

Australia was in a tough spot in late 1940. With international tensions running high, a war against Japan, possibly even a Japanese invasion of the country, seemed like a real possibility. The country needed an armored force, but couldn’t get one from abroad, as Britain needed all the tanks it could build or buy for the war in North Africa and for defense against a possible German invasion. (The Sea Lion That Sank)

Australia decided to develop its own tank – and contrarily to expectations, actually did it. The AC1 (“Australian Cruiser 1”) Sentinel tank was the first one developed in the country, and the only one ever produced in quantity.

The Sentinel was a fascinating design. It was the first tank with a single-piece cast hull in history, a decision born of necessity as Australia didn’t have the industrial capacity to produce and weld rolled steel. They didn’t have proper tank engines, either, so they used three V8 Cadillac engines feeding power to the same drivetrain – it gave the 28-ton vehicle a top speed of 30 mph (48 km/h), which was very respectable in its weight category. The tank combined typically British, American and French design elements, the last one thanks to a French tank designer who helped with the project. 

Now, the Sentinel was far from perfect. The turret was extremely cramped, and its 2-pounder gun was getting long in the tooth by the came the tank rolled off the assembly line. Even so, the fact that Australia, working on its own, could produce a functional tank at all, was remarkable. And, as far as we can tell, the Sentinel might have ended up as a very strong weapon against Japanese light tanks.

The Sentinel never saw action, as Australia started getting British and American tanks by the time Sentinel production could start up in earnest. Only some 65 AC1-s were produced. Later improvements with a larger turret included a larger, 25-pounder gun, a pair of two 25-pounders (only to test if the turret could take the recoil – it could), and even the powerful 17-pounder that later ended up on the Sherman Firefly. (The M4 Sherman)

Possibly much to the chagrin of its designers, however, the Sentinel is not remembered for any of the above. Instead, it is remembered for a single unfortunate piece of design. The tank’s secondary armament was two highly reliable British Vickers machine guns, one sticking out to the front from the center of the hull. The Vickers is a water-cooled gun, and its water jacket had to be protected from hits. A special armor cowling was designed for the gun, and, well… it had an unfortunate appearance. Simply put, it ended up looking like a very rude part of the human anatomy, preserving the Sentinel in memory for the wrong reason.