Australia's Australian Cruiser 1, Australian Cruiser Mk I, AC1, Sentinel

Photos

Design

With Japan becoming a threat in the Pacific and England occupied by Germany, the Australian Ministry of Munitions started to consider building their own tanks in early June 1940.

This was to be a major undertaking by the Australians as they had never even built their own automobiles.

A. Chamberlain, was an engineer that was sent to the United States to study tank production. He was joined by Colonel W. D. Watson, who was an advisor from England. They both studied the M3 Medium.

In November the Australian General Staff developed the requirements for a tank. It was to have a 2-pdr (40 mm) gun and two 7.7 mm (0.303") machine guns. The tank was also required to go 30 mph and have at least 50 mm of armor. It was to use as many of the same components as the American M3 Light Tank. The engine was to be three Cadillac automobile engines joined together. Cast armor was also a requirement.

It had rubber-block suspension with horizontal volute bogies similar to the French Hotchkiss.

The centered hull machine gun had a large armored sleeve.

Fighting Compartments

In the front the driver sat on the right side with the hull gunner on the left. Between them sat the gearbox and the Vickers .303 machine gun that was water cooled.

The middle compartment contained the turret, which contained the commander on the left, the loader / radio operator on the right, and the gunner in front of the commander.

The rear compartment contained the frame which held the three Cadillac 75 engines. The fuel and radiator was also located in the rear compartment.

Hull

As firms producing rolled armored plates were committed, it was decided to try to make the hull from a solid cast. Other experiments involved trying to make strong enough armor from metals available in Australia.

Engine

Early hopes to use the Guiberson diesel engine were dashed and the Cadillac automobile engine was selected. Three engines were combined.

Australia had hoped to make a copy of the M3 Medium's gearbox, but industry in Australia just didn't have the tooling to make them properly. Chamberlain returned in May 1941 from the United States proposing the design of what would become the AC 2. The AC 2 would use imported transmissions that were used in heavy trucks. However, with events in the Pacific rapidly changing, the AC 2 program was cancelled in September 1941 by the Minister for the Army.

With design changes it became possible for the manufacture of the gearbox, for the AC 1, in Australia.

Radio

The radio was a Wireless Set No. 19 Mk 2.

Prototype

A wooden prototype was built in early 1941 and in October the first hull had been cast. The first three pilot models were completed in January 1942, only 22 months after the original General Staff specifications.

AC 3

The AC 1 was originally designed to be capable of carrying the 6 pdr, but supplies were unavailable due to the British Army needing them in North Africa. It was decided to install an Australian produced 25 pdr. The AC 3 was first test fired at Williamstown, Victoria, on June 29, 1942.

Production

The estimated 2,000 would be needed and first ones to be ready by July 1941 and 70 per month being produced.

The Chullona Tank Assembly Shops in New South Wales would produce the tanks. Production started in August 1942 with a total of 66 being built. A new factory was built, but with America able to supply enough tanks for Australia's use production ceased and the tank was used for training.

• AC1: >60, 66
  • Production: 1942 - ?, August 1942 - ?, ? - July 1943

Variants

• AC 1:
• AC 2: Was another design that was dropped after truck components became unavailable from US. Became available in January 1942.
• AC 3: Had 25 pdr howitzer mounted in turret. This had a larger turret ring and turret. The hull MG was removed. The 3 engines were given a single crankcase. Prototypes appeared in early 1943. Never went into production.
• AC 4: Was to have the 17 pdr gun in turret. However, none were available and two 25 pdr guns were installed in the turret to simulate the recoil of the 17 pdr. A prototype was built in mid-1943. One of the prototypes had a torsion bar suspension.

Usage

Used only for training.