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

Photos

Australian Cruiser AC1: Royal Armored Corps Tank Museum
Australian Cruiser AC3:

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 1940.⁶

This was to be a major undertaking by the Australians as they had never even built their own automobiles.⁶

A. Chamberlain, was an engineer that was sent to the United States to study tank production.⁶ He was joined by Colonel W. D. Watson, who was an advisor from England.⁶ They both studied the M3 Medium.^4,6

In November the Australian General Staff developed the requirements for a tank.⁶ It was to have a 2-pdr (40 mm) gun and two 7.7 mm (0.303") machine guns.^5,6 The tank was also required to go 30 mph and have at least 50 mm of armor.⁶ It was to use as many of the same components as the American M3 Light Tank.⁵ The engine was to be three Cadillac automobile engines joined together.⁵ Cast armor was also a requirement.⁵

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

The hull MG had a armored sleeve.

Fighting Compartments

In the front the driver sat on the right side with the hull gunner on the left.⁶ Between them sat the gearbox and the Vickers .303 machine gun that was water cooled.⁶

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.⁶

The rear compartment contained the frame which held the three Cadillac 75 engines.⁶ The fuel and radiator was also located in the rear compartment.⁶

Hull

As firms producing rolled armored plates were committed, it was decided to try to make the hull from a solid cast.⁶ Other experiments involved trying to make strong enough armor from metals available in Australia.⁶

Engine

Early hopes to use the Guiberson diesel engine were dashed and the Cadillac automobile engine was selected.⁶ Three engines were combined.^4,6

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.⁶ Chamberlain returned in May 1941 from the United States proposing the design of what would become the AC 2.⁶ The AC 2 would use imported transmissions that were used in heavy trucks.⁶ However, with events in the Pacific rapidly changing, the AC 2 program was cancelled in September 1941 by the Minister for the Army.⁶

With design changes it became possible for the manufacture of the gearbox, for the AC 1, in Australia.⁶

Radio

The radio was a Wireless Set No. 19 Mk 2.⁶

Prototype

A wooden prototype was built in early 1941 and in October the first hull had been cast.⁶ The first three pilot models were completed in January 1942, only 22 months after the original General Staff specifications.⁶

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.⁶ It was decided to install an Australian produced 25 pdr.⁶ The AC 3 was first test fired at Williamstown, Victoria, on June 29, 1942.⁶

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.^4,6

• AC1: 66^3,6
  • Production: August 1942 - ?³, ? - July 1943⁴

Variants

• AC 1:
• AC 2: Was another design that was dropped after truck components became unavailable from US.⁶ Became available in January 1942.⁴
• AC 3: Had 25 pdr howitzer mounted in turret.⁶ 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.⁶ However, none were available and two 25 pdr guns were installed in the turret to simulate the recoil of the 17 pdr.⁶ A prototype was built in mid-1943. One of the prototypes had a torsion bar suspension.

Usage

Used only for training.

Specifications

		Australian Cruiser Mk I6, AC 16	AC 36	AC 46
Crew	51	Commander, driver, hull gunner, gunner, loader2,6 52,3,4,5,6	Commander, driver, gunner, loader2,6 46, 52
Physical Characteristics
Weight	62,720 lb, 62,732 lb 28 tons1 28,489 kg1	62,720 lb2,3,4,5 28 tons6 28,450 kg4,5	62,720 lb2	31 tons6
Length w/gun	20' 9"1 6.4 m1	20' 9"2,3,4,5,6 6.325 m4,5	20' 9"2
Length w/o gun
Height	9' 1", 8' 5"1 2.59 m1	8' 4.75"4,5,6, 8' 5"2,3 2.56 m4,5	8' 5"2
Width	8' 2", 8' 5", 9' 1"1 2.8 m1	9' 1"2,3,4,5,6 2.768 m4,5	9' 1"2
Width over tracks
Ground clearance	1' 3"
Ground contact length
Ground pressure		13.4 psi6
Turret ring diameter		54"6	64"6	70"6
Armament
Main	40 mm (2 pdr)1	2 pdr. OQF2 2 pdr.3,4,6	25 pdr.2,4,5,6 25 pdr. howitzer3	17 pdr.3,4,5,6
Secondary
MG	2: 7.62 mm MG1	2: Vickers .303 cal MG2,6 2: Vickers MG3 2: 7.7 mm MG4	Vickers .303 cal MG2
MG - coaxial	7.7 mm	Vickers .303 MG6	Vickers .303 cal MG6	Vickers .303 cal MG6
MG - hull	7.7 mm	Vickers .303 MG6
Side arms
Quantity
Main	130	1302,6
Secondary
MG	4,250	4,2502,6
Side arms
Armor Thickness (mm)	651	252, 652, 25 - 263, 25-655	25 - 654 252, 652
Hull Front, Upper		656
Hull Front, Lower
Hull Sides, Upper		456
Hull Sides, Lower
Hull Rear		456
Hull Top		256
Hull Bottom
Turret Front		656
Turret Sides		656
Turret Rear		656
Turret Top		256
Engine (Make / Model)	3: Cadillac1	3: Cadillac2,3,4,5 3: Cadillac 756	3: Cadillac2 3: Perrier-Cadillac 41-756	4: Gipsy Major6
Bore / stroke
Cooling		Water6
Cylinders	81 x 31	V-82,3,6	V-82
Capacity
Net HP	1171 x 31	117 each2,3 3304,5, 350@3,050 rpm6	3972
Power to weight ratio		12:1 hp/ton6
Compression ratio
Transmission (Type)
Steering
Steering ratio
Starter
Electrical system		Lights: 6 volt6 Radio: 12 volt6 Turret traverse: 40 volt6
Ignition
Fuel (Type)	Gasoline1	Gasoline2,4,5	Gasoline2
Octane
Quantity		140 gallons internal6 44 gallon jettisonable tank6
Road consumption
Cross country consumption
Performance
Traverse		360°2,6 , 18°/second6	360°2
Speed - Road	20 mph, 30 mph1 48 kph1	20 mph3, 30 mph2,4,5,6 48.2 kph4,5	30 mph2
Speed - Cross Country		20 mph2	20 mph2
Range - Road	200 miles, 198 miles1 319 km1	200 miles2,4,5,6 322 km4,5	229 miles2
Range - Cross Country
Turning radius
Elevation limits
Fording depth	3' 11.5"	4'2	4'2
Trench crossing	8'	8'4,5,6, 9' 6"2 2.438 m4,5	9' 6"2
Vertical obstacle		2'2	4'2
Climbing ability
Suspension (Type)	Volute Scissors	Horizontal volute spring6
Wheels each side	6x2	3x2 sets6
Return rollers each side	3	36
Tracks (Type)		Rubber6 Steel6
Length
Width	16.5"	16.5"2,6	16.5"2
Diameter
Number of links		Rubber: 866 Steel: 1296
Pitch		Rubber: 6"6 Steel: 4"6
Tire tread
Track centers/tread		7' 6.5"2,6	7' 6.5"2