AC1 Sentinel Fast Tank

 Australia

AC1 Sentinel fast tank

After the outbreak of war in Europe on September 1, 1939, the Australian government asked Britain to supply various types of armaments, including tanks. It was assessed that the threat could be Japan, which does not hide its aggressive plans towards Australia and the entire region of Southeast Asia.

Preserved AC I on display at the RAAC museum – Credits: Wikimedia Commons

 

 In the autumn of 1939, Britain had no surplus armaments, especially modern ones, and could not help its dominions. In addition, in June 1940, after the fall of France and the defeat of the British Expeditionary Force, all its armor and heavy weapons, then the best in the British army, remained on the beaches of Dunkirk. For Australia, the only real possibility to quickly increase its defense potential was to place orders for weapons in the USA. In 1940, only the now obsolete M2 light tank was available. It wasn't until 1941 that the production of the new M3 General Stuart light tank began and it was shipped to Australia. 

The AC I under construction at the Chullora tank annex. (Source:- Australian War Memorial)

 

 

At the same time, a group of engineers was working on a tank project that was supposed to meet the requirements of tactical-techn. specified by the General Staff of the Australian Army in November 1940. In order to speed up the design work, it was planned to use components of the M3 medium tank, which was introduced into production in the USA in 1941. Plans to start its license production in Australia fell through, so the design of the tank was resumed based on own forces and local industrial potential. The new tank was designated AC1 (Australia Cruiser 1), meaning it was supposed to be a fast tank. The hull of the prototype was ready in October 1941, and the entire vehicle in January 1942. The tests, research and improvement of the structure lasted over a year. The tank was named Sentinel and its serial production began in August 1942 at Chullon Tank Assembly in New South Wales. It was a unique achievement because from the time the order was placed only 22 months had passed and Australia had no experience in tank design or production.

RAAC tank crew on their new Australian Cruiser Tank AC1 Sentinel

By July 1943, 66 AC1 Sentinel tanks had been produced, but then the better armed and armored M3 and M4 tanks, purchased in the USA, were already entering the armament of the Australian army. The 40 mm gun was ineffective against most Japanese tanks and was not suitable for fighting against infantry and fortifications (no high-explosive shells). At that time, the AC3 version was developed, armed with an 87.6 mm (25-pounder) field gun, manufactured in Australia. Unfortunately, it was not very suitable for fighting tanks. In this situation, in mid-1943, Australian designers equipped the AC tank with an anti-tank gun. 76.2 mm (17-pounder). However, the production of the tank - designated AC4 - was not undertaken because deliveries of equally good, mass-produced American tanks continued.

Source: https://www.reddit.com/r/interestingasfuck/comments/s8a1c8/the_aci_sentinel_an_australian_tank_design_meant/

 

The AC1 Sentinel fast tank had a hull made of joined cast parts. In the left side wall of the hull, between the carriages of the road wheels and the upper part of the track, there was an escape hatch. The thickness of the hull armor ranged from 25 to 65 mm. Combat weight - 28.45 t. The turret of a characteristic, slightly flattened, oval shape was cast. The thickness of the frontal part of the armor and armament yokes was 65 mm. In the front part of the hull, on the left, sat the driver, and next to him, on the right - the gunner who operated the front, hull-mounted 7.7 mm Vickers machine gun. They had rotating observation periscopes. The driver could also observe the terrain through a rectangular hatch in the frontal armor or through the observation slit. Two headlights were placed on the fenders. Two towing hooks were attached to the front and rear hull plates.

Sentinel AC1

The three-person turret could be rotated by an electric motor, powered by a generator driven by the tank engine, or it could be manually rotated in emergency mode. In the right part of the turret there was a loader's station, which also operated a radio station mounted at the rear of the turret. In the left part of the turret there was a gunner's station, and behind him - the tank commander. The commander had a small observation turret with periscopes. There was only one two-piece hatch in the turret (in the commander's turret).

Source: www.tankarchives.ca

The main armament of the tank was placed in the turret - the 40 mm OQF Mk IX cannon and the 7.7 mm Vickers machine gun coupled with it. The cannon yoke was very characteristic, clearly protruding in relation to the turret. 140 cannon rounds were carried in the tank. The AC1 Sentinel fast tank was powered by three 8-cylinder, carbureted, liquid-cooled Cadillac engines mod. 75 with 117 hp (86 kW) each. The gearbox had four forward ratios and one reverse ratio. The maximum speed on the roads was high - 48 km/h.

Source: www.tankarchives.ca

The undercarriage (similar to the Hotchkiss H-35 tank) consisted of 12 twin road wheels, a pair of idler wheels at the rear and a pair of driving wheels at the front. The road wheels were grouped in pairs in 6 bogies amortized with spring springs. The road wheels and tension wheels had rubber bandages. The upper part of the track rested on three supporting rollers. The track width was 419 mm.

• Crew: 5
• Weight: 28.45 tons 
• Dimensions: length 6.325 m, width 2.77 m, height 2.565 m 
• Engine: three 8-cylinder, carburettor, water-cooled, Cadillac mod. 75 with 117 hp (86 kW) 
• Performance: max. road speed 48 km/h, max. range 320 km
• Overcome obstacles: fords 1.2 m, vertical walls 0.6 m, ditches 2.8 m 
• Armament: 1x 40mm Mk IX gun, 2x 7.7mm Vickers