Sentinel tank
Encyclopedia
The Sentinel tank was a cruiser tank
designed in Australia
in World War II
in response to the war in Europe, and to the threat of Japan expanding the war to the Pacific or even a feared Japan
ese invasion
of Australia. It was the first tank to be built with a hull cast as a single piece, and the only tank to be produced in quantity in Australia. The few Sentinels that were built never saw action as Australia's armoured divisions
had been equipped by that time with British and American tanks.
gun-equipped design in November 1940, and was initially intended to be a true Cruiser tank
. Like the Canadian Ram
the Australian Cruiser was to be based on the engine, drive train, and lower hull of the American M3 Medium
tank, mated to an upper hull and turret built closely along the lines of a British Crusader
. By 1942, trying to keep pace with German tanks, the design specification had become more like an American medium tank
.
Due to a lack of home grown experience in tank design a mission was sent to the US to exmaine the M3 design and Colonel W.D. Watson MC, an artillery officer with many years tank design experience was provided by the UK. He arrived in December 1940.
The Australian Cruiser tank Mark 1 (AC1) was designated "Sentinel" in February 1942. Fabrication was by Sydney's Chullora Tank Assembly Shops with serial production vehicles emerging in August 1942, the premises also being used as a testing ground. The design used existing parts where available from other tank designs, simplified where necessary to match the machining capacity present in Australia. The hull was cast as a single piece, as was the turret; a technique not used on the hull of any other tanks of the era.
The original vehicle was designed to mount a QF 2 pounder
this was later changed to a QF 6 pdr
(57 mm, 2.25 in). However none of these were available and the first 65 tanks were built with the 2 pounder. Two Vickers machine gun
s were carried as secondary armament, one in the hull and a second mounted coaxially beside the main gun. The preferred engines suitable to power a 28 tonne tank, a Pratt & Whitney Wasp
single row petrol radial, or a Guiberson diesel radial, were not available within Australia, so the Sentinel was powered by the combined output of three Cadillac
346 in³ (5.7 L
) V8
petrol car engines installed in clover-leaf configuration (two engines side-by-side to the front and a single to the rear: all three feeding a common gearbox). Sixty-five production vehicles had been completed by June 1943.
.jpg)
The Sentinel was to be succeeded by the AC3, a much improved design with better armour protection, and most importantly increased firepower. The next step up in firepower available in Australia was the 25 pounder (87.6 mm, 3.45 in) gun-howitzer
. This was quickly redesigned as a tank gun, work that would later prove useful for the design of the Short 25 Pounder
. Mounted in a fully traversable turret larger than that of the AC1 but using the same 54 inch (137 cm) turret ring, it was slightly cramped for the turret crew but gave the AC3 both armour piercing capability as well as an effective high explosive round. The hull machine gun and gunner were removed from the design to make room for stowage of the larger 25 pounder ammunition. Powered by the same three Cadillac V8 engines as the AC1, they were now mounted radially on a common crank case and geared together to form the "Perrier-Cadillac", a single 17.1 L, 24 cylinder engine, very similar in some respects to the later A57 Chrysler multibank used in some variants of the US M3 and M4 tanks. One pilot model AC3 had been completed and work had started on producing 25 tanks for trials when the programme was terminated.
In an effort to further improve the firepower of the Australian produced tanks, a turret was developed and mounted on one of the earlier development vehicles to assess the vehicle's ability to mount the foremost Allied
anti-tank gun of the day – the British 17 pounder
(76 mm, 3 in). This was achieved by mounting two 25 pounder gun-howitzers which when fired together would significantly exceed the recoil of a 17 pounder. It was later fitted with a 17 pounder and after successful gunnery trials the 17 pounder was selected for the AC4 design. The engine was larger - constructed from four Gipsy Majors provided by Holden.
The completed Sentinel tanks were used for evaluation purposes only and were not issued to operational armoured units. The Australian Cruiser tank programme was terminated in July 1943 believing it better for Australia to put the effort spent on the AC tanks towards building her own railway locomotives and and supporting the large number of US tanks due to arrive. The tanks that had been produced were placed in storage until the end of the war. In 1943 the 3rd Army Tank Battalion
was equipped with a squadron of AC1 tanks which had been modified to resemble German tanks. These tanks were used in the filming of the movie 'The Rats of Tobruk'. This appears to have been the only time a squadron of Sentinels was used for any purpose.
All but three tanks were dismantled or disposed of in 1945. Surviving Sentinels can be seen at the RAAC tank museum at Puckapunyal Victoria (serial number 8030), and at the Bovington Tank Museum
(serial number 8049). The only completed AC3 (serial number 8066) is located at the Treloar Technology Centre at the Australian War Memorial
in Canberra.
.jpg)
Cruiser tank
The cruiser tank was a British tank concept of the inter-war period. This concept was the driving force behind several tank designs which saw action during the Second World War....
designed in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
in response to the war in Europe, and to the threat of Japan expanding the war to the Pacific or even a feared Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese invasion
Invasion
An invasion is a military offensive consisting of all, or large parts of the armed forces of one geopolitical entity aggressively entering territory controlled by another such entity, generally with the objective of either conquering, liberating or re-establishing control or authority over a...
of Australia. It was the first tank to be built with a hull cast as a single piece, and the only tank to be produced in quantity in Australia. The few Sentinels that were built never saw action as Australia's armoured divisions
Australian Armoured Units of World War II
Armoured units made a relatively small, but important, contribution to Australia’s war effort during World War II. While Australia formed three armoured divisions and two independent armoured brigades during the war, Australian armoured units only saw action as independent regiments and companies...
had been equipped by that time with British and American tanks.
History
The AC1 began as a 2 pounderOrdnance QF 2 pounder
The Ordnance QF 2-pounder was a British anti-tank and vehicle-mounted gun, employed in the Second World War. It was actively used in the Battle of France, and during the North Africa campaign...
gun-equipped design in November 1940, and was initially intended to be a true Cruiser tank
Cruiser tank
The cruiser tank was a British tank concept of the inter-war period. This concept was the driving force behind several tank designs which saw action during the Second World War....
. Like the Canadian Ram
Ram tank
The Tank Cruiser, Ram was a cruiser tank designed and built by Canada in the Second World War, based on the U.S. M3 Medium tank. Due to the entrance of the United States into the war and the superior design of the American Sherman, it was used exclusively for training purposes and was never used in...
the Australian Cruiser was to be based on the engine, drive train, and lower hull of the American M3 Medium
M3 Lee
The Medium Tank M3 was an American tank used during World War II. In Britain the tank was called "General Lee", named after Confederate General Robert E. Lee, and the modified version built with a new turret was called the "General Grant", named after U.S. General Ulysses S. Grant.Design commenced...
tank, mated to an upper hull and turret built closely along the lines of a British Crusader
Crusader tank
The Tank, Cruiser, Mk VI or A15 Crusader was one of the primary British cruiser tanks of the early part Second World War and perhaps the most important British tank of the North African Campaign...
. By 1942, trying to keep pace with German tanks, the design specification had become more like an American medium tank
Medium tank
Medium tank was a classification of tanks; the medium being intermediate in size and weight and armament between heavy tanks and light tanks.The medium tank concept has been eclipsed by the main battle tank.-History:...
.
Due to a lack of home grown experience in tank design a mission was sent to the US to exmaine the M3 design and Colonel W.D. Watson MC, an artillery officer with many years tank design experience was provided by the UK. He arrived in December 1940.
The Australian Cruiser tank Mark 1 (AC1) was designated "Sentinel" in February 1942. Fabrication was by Sydney's Chullora Tank Assembly Shops with serial production vehicles emerging in August 1942, the premises also being used as a testing ground. The design used existing parts where available from other tank designs, simplified where necessary to match the machining capacity present in Australia. The hull was cast as a single piece, as was the turret; a technique not used on the hull of any other tanks of the era.
The original vehicle was designed to mount a QF 2 pounder
Ordnance QF 2 pounder
The Ordnance QF 2-pounder was a British anti-tank and vehicle-mounted gun, employed in the Second World War. It was actively used in the Battle of France, and during the North Africa campaign...
this was later changed to a QF 6 pdr
Ordnance QF 6 pounder
The Ordnance Quick-Firing 6-pounder 7 cwt, or just 6 pounder, was a British 57 mm gun, their primary anti-tank gun during the middle of World War II, as well as the main armament for a number of armoured fighting vehicles...
(57 mm, 2.25 in). However none of these were available and the first 65 tanks were built with the 2 pounder. Two Vickers machine gun
Vickers machine gun
Not to be confused with the Vickers light machine gunThe Vickers machine gun or Vickers gun is a name primarily used to refer to the water-cooled .303 inch machine gun produced by Vickers Limited, originally for the British Army...
s were carried as secondary armament, one in the hull and a second mounted coaxially beside the main gun. The preferred engines suitable to power a 28 tonne tank, a Pratt & Whitney Wasp
Pratt & Whitney R-1340
|-See also:* Pratt & Whitney Wasp series* Pratt & Whitney R-985 Wasp Junior* Pratt & Whitney R-1535 Twin Wasp Junior* Pratt & Whitney R-1830 Twin Wasp-Bibliography:...
single row petrol radial, or a Guiberson diesel radial, were not available within Australia, so the Sentinel was powered by the combined output of three Cadillac
Cadillac
Cadillac is an American luxury vehicle marque owned by General Motors . Cadillac vehicles are sold in over 50 countries and territories, but mostly in North America. Cadillac is currently the second oldest American automobile manufacturer behind fellow GM marque Buick and is among the oldest...
346 in³ (5.7 L
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...
) V8
V8 engine
A V8 engine is a V engine with eight cylinders mounted on the crankcase in two banks of four cylinders, in most cases set at a right angle to each other but sometimes at a narrower angle, with all eight pistons driving a common crankshaft....
petrol car engines installed in clover-leaf configuration (two engines side-by-side to the front and a single to the rear: all three feeding a common gearbox). Sixty-five production vehicles had been completed by June 1943.
Howitzer
A howitzer is a type of artillery piece characterized by a relatively short barrel and the use of comparatively small propellant charges to propel projectiles at relatively high trajectories, with a steep angle of descent...
. This was quickly redesigned as a tank gun, work that would later prove useful for the design of the Short 25 Pounder
Ordnance QF 25-pounder Short
The Ordnance QF 25-pounder Short was an Australian variant of the British Ordnance QF 25-pounder field gun/howitzer. The gun was developed by modifying the 25-pounder's design to improve its mobility during jungle warfare. Development began in 1942, and the weapon first entered service with the...
. Mounted in a fully traversable turret larger than that of the AC1 but using the same 54 inch (137 cm) turret ring, it was slightly cramped for the turret crew but gave the AC3 both armour piercing capability as well as an effective high explosive round. The hull machine gun and gunner were removed from the design to make room for stowage of the larger 25 pounder ammunition. Powered by the same three Cadillac V8 engines as the AC1, they were now mounted radially on a common crank case and geared together to form the "Perrier-Cadillac", a single 17.1 L, 24 cylinder engine, very similar in some respects to the later A57 Chrysler multibank used in some variants of the US M3 and M4 tanks. One pilot model AC3 had been completed and work had started on producing 25 tanks for trials when the programme was terminated.
In an effort to further improve the firepower of the Australian produced tanks, a turret was developed and mounted on one of the earlier development vehicles to assess the vehicle's ability to mount the foremost Allied
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
anti-tank gun of the day – the British 17 pounder
Ordnance QF 17 pounder
The Ordnance Quick-Firing 17 pounder was a 76.2 mm gun developed by the United Kingdom during World War II. It was used as an anti-tank gun on its own carriage, as well as equipping a number of British tanks. It was the most effective Allied anti-tank gun of the war...
(76 mm, 3 in). This was achieved by mounting two 25 pounder gun-howitzers which when fired together would significantly exceed the recoil of a 17 pounder. It was later fitted with a 17 pounder and after successful gunnery trials the 17 pounder was selected for the AC4 design. The engine was larger - constructed from four Gipsy Majors provided by Holden.
The completed Sentinel tanks were used for evaluation purposes only and were not issued to operational armoured units. The Australian Cruiser tank programme was terminated in July 1943 believing it better for Australia to put the effort spent on the AC tanks towards building her own railway locomotives and and supporting the large number of US tanks due to arrive. The tanks that had been produced were placed in storage until the end of the war. In 1943 the 3rd Army Tank Battalion
Australian 3rd Army Tank Brigade
The 3rd Army Tank Brigade was an armoured brigade of the Australian Army during the Second World War. The Brigade was formed in May 1942 and disbanded in September 1943.-History:...
was equipped with a squadron of AC1 tanks which had been modified to resemble German tanks. These tanks were used in the filming of the movie 'The Rats of Tobruk'. This appears to have been the only time a squadron of Sentinels was used for any purpose.
All but three tanks were dismantled or disposed of in 1945. Surviving Sentinels can be seen at the RAAC tank museum at Puckapunyal Victoria (serial number 8030), and at the Bovington Tank Museum
Bovington Tank Museum
The Tank Museum is a collection of armoured fighting vehicles in the United Kingdom that traces the history of the tank. With almost 300 vehicles on exhibition from 26 countries it is the second-largest collection of tanks and armoured fighting vehicles in the world.The Musée des Blindés in France...
(serial number 8049). The only completed AC3 (serial number 8066) is located at the Treloar Technology Centre at the Australian War Memorial
Australian War Memorial
The Australian War Memorial is Australia's national memorial to the members of all its armed forces and supporting organisations who have died or participated in the wars of the Commonwealth of Australia...
in Canberra.
Variants
- AC I "Sentinel"
- one 2 pounderOrdnance QF 2 pounderThe Ordnance QF 2-pounder was a British anti-tank and vehicle-mounted gun, employed in the Second World War. It was actively used in the Battle of France, and during the North Africa campaign...
gun (130 Rounds) - two Vickers machine gunVickers machine gunNot to be confused with the Vickers light machine gunThe Vickers machine gun or Vickers gun is a name primarily used to refer to the water-cooled .303 inch machine gun produced by Vickers Limited, originally for the British Army...
s (4,250 Rounds) - three Cadillac V8 engines mounted two abreast, and one centrally behind them
- one 2 pounder
- AC III "Thunderbolt"
- one 25 pounder gun (120 rounds)
- one Vickers machine gun
- Crew reduced to 4 with the removal of the hull MG from the design
- three Cadillac V8 engines mounted on a common crank case
- AC IV
- one 17 pounderOrdnance QF 17 pounderThe Ordnance Quick-Firing 17 pounder was a 76.2 mm gun developed by the United Kingdom during World War II. It was used as an anti-tank gun on its own carriage, as well as equipping a number of British tanks. It was the most effective Allied anti-tank gun of the war...
or 25 pounder gun - one Vickers machine gun
- Engine as Mark III
- one 17 pounder