Cruiser Mk III (AC3) Tank

Discussion in 'Weapons, Technology & Equipment' started by spider, May 16, 2009.

  1. spider

    spider Very Senior Member

    1943 - An Australian developed and built Cruiser Mk III (AC3) tank, fitted with two 18 pounder guns in the turret.

    Spider
     

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  2. Tom Canning

    Tom Canning WW2 Veteran WW2 Veteran

    Spider
    .................and he must havebeen pretty well stoned out of his mind to do so - in using the bottom end of a sherman with an ugly looking turret - thank god that didn;'t go too far...
    Cheers
     
  3. Peter Clare

    Peter Clare Very Senior Member

    I believe this to be a Cruiser Mk II. Could be wrong as tanks are not my department.


    [​IMG]
     
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  4. phylo_roadking

    phylo_roadking Very Senior Member

    Not a Sherman - an Australian Sentinel hull, originally based on the M3...

    [​IMG]

    This was a design started late in 1940 for a tank intended for Australian production utilising only readily available materials and sources. Commercial truck engines were to be used, together with an adapted bersion of the American M3 Medium Tank final drive and transmission. Cast hull and turret with 2pdr gun were features of the finalised design. Work on the AC I was held back for a time while an alternative design AC II was studied. The AC II was considered too complicated to build and was dropped. The AC I design was completed in September 1941 and the prototype was finished in January 1942. Production started in August 1942 and 66 vehicles were built. These were used only for training as there were by then plenty of American medium tanks available to equip Australian units in the field. The design was very sound with excellent armor. Note the Hotchkiss inspired suspension and the American tracks. The AC III was a close support version. The 25pdr gun required a larger turret ring and turret. The hull MG was eliminated and the triple engines were given a common crankcase. The prototype was tested early in 1943, however there was no production. The AC IV was a further developement of the AC III fitted with a 17pdr gun. Pending the availability of the 17pdr gun, twin 25pdr guns were fitted in order to simulate the high recoil of the 17pdr for test purposes. One test vehicle in the AC series was fitted with torsion bar suspension but did not proceed beyond prototype stage. Dimentions of the AC III and IV were generally similar to the AC I.
     
  5. von Poop

    von Poop Adaministrator Admin

    As Phylo references, I think that top ac is the '3' fitted with twin 25pdrs, the remarkable 'Sentinel' hull (advanced casting for it's time) was deemed to accommodate the recoil of both guns 'with ease'. And they were said to give 20% more recoil force than the envisioned 17pdr.
    Christ knows what it was like in the turret when both fired at once though.

    Don't think I've seen that picture of it... (if it is the twin 25s and not some other experiment) - Nice one.
    Cropped up here before:
    Ram Tank
    25pdr
    Strange Vehicles

    They should probably be referred to as 'Australian Cruiser' to avoid the confusion with the British Cruiser series as Peter posted.

    ~A
     
  6. phylo_roadking

    phylo_roadking Very Senior Member

    Hmm...can you imagine the damage it could have done if the guns were aligned to converge at a few hundred yards, like fighter aircraft???

    It would have been a HELL of a tank killer...with a low profile, and fast at a genuine 30mph!
     
  7. von Poop

    von Poop Adaministrator Admin

    It's almost a shame the 'Sentinels' never saw action.
    I get the impression the Aussies would have had something to be proud of in that machine.

    'AC4' - The prototype that was actually fitted with a 17pdr:
    [​IMG]
    ac4-prototype.jpg
     
  8. phylo_roadking

    phylo_roadking Very Senior Member

    Yes, they seem to have had a rep for reliability, and that low profile gave it quite an advantage over the equivalent M3/M4/Ram. The drive train is reliable - Hotchkiss-style suspension, Sherman tracks...and that tough cast hull. It's just a pity Australia's lack of heavy industry meant they couldn't consider producing the sort of numbers they would have needed for active service. It certainly out-spec's most British types of 1943!!!

    P.S. look in the background of that pic - is that a gun carriage one of the two 25pdrs were stripped out of for the testing prototype???

    Another view of the 17pdr prototype -

    [​IMG]

    The big round hole in the glacis is where the hull gun, mounted in a strange armoured barbette in the "standard" Sentinel, was removed, along with the gunner behind it, to make room for the 25pdr HE ammo in the two-gun prototype.

    I have to admit - it's cute. Imagine that with track guards, and that gurt big hole replaced by a smooth sloping glacis...it would look suprisingly 1950s-ish!!!

    Unfortunately - not only did cheaper imports become available during the Sentinel's looooong three-year gestation period - The Australians' armour requirements had changed; in 1940 they wanted a Cruiser, and in late 1940 and most of 1941 it would indeed have been invaluable to them in North Africa - but by the time it became available, Australian armour had become Matildas and Valetines slugging through the jungles of New Guinea...sometimes moving just a few hundred yards a day then bogging down as a gun-armed strongpoint.
     
  9. Smudger Jnr

    Smudger Jnr Our Man in Berlin

    This thread is seriously enjoyable reading.

    This tank had the makings of a class act, just a pity that it never made it into production.

    Regards
    Tom
     
  10. phylo_roadking

    phylo_roadking Very Senior Member

    This thread is seriously enjoyable reading.

    This tank had the makings of a class act...


    HOWEVER....there WAS one major fly in the ointment...

    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. Sixty-five production vehicles had been completed by June 1943.
    <SUP></SUP>
    Powered by the same three Cadillac V8 engines as the AC1, they were now mounted 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.


    ...it was hampered by engine availability on the other side of the world. Can you further imagine what it would have been like re-engineered to take an RR Meteor???;) As fast as a Cromwell, very nearly as well armoured, and certainly as hard a hitter if not better for a time.

    Interestingly - that engine combo produced 330 hp to the Cromwell's 600; so for just over HALF the power, the Sentinel produced three-quarters of the speed of the Cromwell. Yet both vehicles weighed the same, at 28 long tons. Engine and transmission changes -

    The "Perrier-Cadillac" power unit was completely new, the three V8 Cadillac engines for the AC1 design were kept but instead of the two abreast and one behind "clover leaf" layout the three engines were mounted around a common crank case to form a single 24 cylinder unit. This saved space and eliminated the three in one out transfer box, resulting in reduced losses through the drive train. This and the use of 80 octane fuel boosted the output of the power unit

    ...to the ACIII prototype boosted the Sentinel's power output to 397 hp. The intended ACIV with the 17pdr gun would have been faster again -

    The weight of the tank had increased to around 32 tonnes but nominal ground pressure was lower than the AC3 due to increased track contact area. Top speed was to be increased to 56km/h (35mph) by planned changes the gearbox gear ratios


    There was even a plan discussed to couple FOUR Gipsy Major in-line aero engines together to provide even MORE power!
     
  11. von Poop

    von Poop Adaministrator Admin

  12. phylo_roadking

    phylo_roadking Very Senior Member

    (nice site - Australian index)


    With a VERY telling comment buried away in the Sentinel istory....

    Lend Lease authorities in the United States had been exerting pressure on Australia for some time to standardise it’s tank production on the M4 or T20 in order to streamline supply and maintenance. Unless Australia agreed to switch over to a US design it would receive no more assistance in this programme in the way of components or machine tools from the US.

    :mad: "Allies"....

    The Australian Government had agreed in late '42 in principle, like it's allies, to the production of a standard tank but when faced with the fact that both the M4 and T20 were significantly more complex than any of the Australian Cruisers, would require twice the man-hours to manufacture, used armaments and ammunition that were not in production in Australia and engines that would have to be imported the programme was terminated, allowing the diversion of manpower to other tasks


    So in the end Australia didn't build Shermans OR T20s EITHER! So much for the politics that had cost them the Sentinel!
     
  13. phylo_roadking

    phylo_roadking Very Senior Member

    One other VERY interesting fact from that article...

    Australian Zirconium-Alloy Cast Armour specification
    Brinell Hardness: 230-240.
    Izod Impact Strength: 20ft/lb rising through production to 52ft/lb.
    Ultimate Tensile Strength: 756MPa (49 T/sq inch). Purposely kept low to reduce spalling.
    This armour was developed specifically for the Australian Cruiser Tank, it's formulation was based on the Australian Bullet Proof Plate armour as used for Australian built Universal Carriers, the Dingo scout car, and other projects. Unlike armour produced in other countries the Australian cast armour contained no nickel as there was no source for this in Australia. Similar to British IT90 cast armour it was slightly softer but much tougher, resulting in less spalling from hits. When an AC1 turret was compared against a specially imported M4 turret the armour proved at least as good the American armour if not better


    Meanwhile...the Sherman weighed in at a slightly heavier 30 tons+, had fractionally thinner armour...and only made around 25mph in most marks!
     
  14. spider

    spider Very Senior Member

    They seemed to have taken a lot of (dumped?) M3 Grants from the US.

    Not sure if they saw operational service in the Pacific, however were used extensively for training.

    Once again ended up in storage in Bandiana Victoria.

    The details of the original photo is the one from description, so cannot attest to its accuracy. However they MAY have used 18P QF barrels as a trial.

    The thought of twin mounted guns is amazing, and a low silhouette.

    Spider
     
  15. spider

    spider Very Senior Member

    Double 25 pounder field gun/howitzer armed test vehicle
    The twin 25 pounder armed tank was a test vehicle only. As a 17 pounder was not available at the time two 25 pounders were fitted into a turret mounted on the development hull E1 by a 163cm (64 inch) turret ring. The intent was to test the recoil system and turret ring by significantly exceeding the recoil force of a single 17 pounder anti-tank gun. The pair of 25 pounders fired together produced approximately 120% of the recoil force of a single 17 pounder anti-tank gun. The tank survived and was subsequently armed with a 17 pounder.

    Perhaps they also trialled an 18P as was a consideration at the time.

    Spider

    Caption:Despite being roughly the same weight as the M3 medium to it's left, the Sentinel presents a frontal target area only about the same size as the M3 Light to it's far left.
     

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  16. Richard G

    Richard G Junior Member

    Bit of a bump to note that the 17 pdr as used in the Sentinel had a revised recoil system, as can be seen in the pics above, which meant that it could be conventionally mounted in the turret. With no loading disadvantages like the Firefly had.
     
  17. Dave55

    Dave55 Atlanta, USA

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  18. canuck

    canuck Closed Account

  19. Chris C

    Chris C Canadian

    The M4A4 had five...
     

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