Australian Military Vehicles Research
The First Australian Sentinel Tank by Michael Koudstaal
Parked out side John Belfield’s Melbourne tank museum sits the remains of the first Australian Cruiser Tank ever built. This is the E1, the first of the three developmental "E series" prototypes for the Australian Cruiser Tank (AC) Mk 1 "Sentinel". This particular vehicle featured a multipart cast hull, a one piece turret and was powered by three Cadillac V8 car engines. The primary task for this vehicle was automotive tests to verify that the power plant and drive train was up to the job of pushing a 28 tonne tank around. This it performed well achieving a top speed of over 64 km/h (40 mph) and racking up more than 2,400 km (1,500 miles) total distance covered. Probably because it used a multiple part construction which allowed for the turret ring diameter to be increased by simply unbolting and replacing one casting, this tank was used first to proof the recoil system for the 17 pounder using a pair of 25 pounder field gun-howitzers (the single 25 pounder itself having previously been tested in the E2) before being armed with a British-designed Australian-made 17 pounder anti-tank gun. Design work for an experimental 17 pounder armed turret had begun in August 1942 and the vehicle was tested in January 1943. This would have made it the most powerfully armed tank in Australia until the arrival of the Centurion nearly a decade later.
The lower hull of the E1 as it was in December 2002. Sitting on top is a shot-up AC3 turret.
Only the lower hull and suspension remain at the museum the upper hull castings have been removed at some point as well as most of the internal gear including the engines. Various other bits and pieces have been removed, including the right hand side drive sprocket which I believe to have ended up on John's rebuilt AC1. Sitting on top of a couple of steel beams is one of several AC3 turrets I understand to have been recovered from the Holsworthy range where John also got the hull and turret for his AC3.
The right hand side of the Axel Housing with the final drive and cover removed.
The rough surface of the armour castings of the hull is immediately apparent. Cast in sand, the armour acquired it's surface texture from the mould and inevitably ended up with grains of sand impregnated throughout the metal. While the American M3 medium and even early M4s had a three piece transmission cover, the ACs right from the start had a single casting that formed the what was referred to as the Axel Housing (Hence the prominent raised lettering on the front of production vehicles BK AH followed by it's sequential casting number). I have been told that on the M3 the armour needed to be assembled around the Cletrac type controlled differential while Australian engineers had figured out a way to assemble the differential from the side allowing the use of a single piece casting. I neglected to check if the differential and brakes were still inside.
The AC E1's gearbox.
The Australian Cruisers were intended to be, like the Canadian "Ram", based on the American M3 Medium lower hull, suspension, engine and drive train. Supply difficulties and a very small industrial base forced Australia to change the design of these components and the ACs ended up very different, particularly the engine. The Australian Cruiser gearbox differs more in detail than design, and the M3 in its ancestry shows. Surprisingly enough it would seem that the original gearbox is still in the tank, the aluminium plate riveted to the housing here (at the rear just under the lifting eye) states that this particular unit is for demonstration purposes only. This is presumably one of the first gearboxes produced and does have some visible differences to the few other AC gearboxes that I have seen. On the far side are the bolts securing the leading bogie.
The right hand side 1st bogie and oval emergency escape hatchway.
The bogies on the E series differ from the production version in having a trailing return roller, why it was designed this way is a mystery to me as even the M3 Medium bogies on which these were originally based had a centrally located return roller. One problem with this arrangement was as the steel tracks first fitted to this vehicle became worn and started to sag the guide horns would begin to first rub against and then wear through the leading edge of the bogie bracket. On production vehicles the return roller was moved to the centre of the bracket to eliminate this problem. The road wheels have no holes in the dish, a distinct difference from production versions which had 4, 6, or even 8 holes present in the dish, with 4 being the most common. Behind the leading bogie on both sides is an oval shaped escape hatch.
The right hand side Tensioning Idler Bracket.
The Idler wheel itself has been removed but the bracket remains showing how it is attached to the hull and actually adjusted. Running along the top here are the recessed slots that allow accesss to the bolts located roughly along the centreline of the armour.
AC E1's rear
Running along the top of the lower hull sides of the engine bay is what would seem to be a shallow tongue-and-groove system to help lock the engine bay superstructure in place. Only the engine compartment has this feature, the forward crew compartment sections have a simple internal flange. The E1 like production AC1s had a seperate "tail" casting that protected the rear air vents by projecting beyond the rear of the hull and over hanging it slightly. On production AC1s this was held on by 5 large bolts, here ti seems to have only 3. On the AC3 this tail section was made as part of the hull casting.
The rear of the AC3 turret number 125.
Since we are here we might as well examine the turret. As has already been mentioned this is an Australian Cruiser Tank Mk 3 turret. Cast onto the back of every turret as part of the casting process is the casting firm's identifier, the casting type and the number of that type, in this case it was made by Bradford Kendall Ltd and is turret casting number 125. John also has T 126 sitting on his AC3 indoors and a third sitting outdoors on an AC1 hull. This turret has taken a significant amount of what looks to me like machinegun fire on the right hand side. All AC turrets had air vents in the back corners of the turret, on the underside of the turret bustle on both sides of the Mk 19 wireless set. Here on the left a direct hit has broken away part of the casting, revealing the walls to the front and also the side that were to protect the crew and wireless set from fragments that might have entered through the vent. The vent itself like all vents on the Australian Cruisers were protected by heavy wire mesh grills.
A side view of turret number 125.
The AC3 turret has several identifying features that set it apart from an AC1 type. Seen here is the extended turret bustle and loader's side pistol port. Up and just ahead of the pistol port is a small bulge to accommodate the loaders periscope. The turret also seems to have been hit by fragments from High Explosive shells. What isn't really visible here are the several HESH hits on the lower side (next time I'll have to beg, borrow or steal a digital camera!), on the inside there is considerable spalling from these hits maybe 20mm deep and 20cm across.
The top of turret number 125.
Part of the turret here has been cut away for what ever reason, the rest of the front left has simply been blown away. Next to the commander's cupola is a small hump to allow for clearance around the 25 pounder breach when firing at maximum depression. On the left of the photo is the hole for the loaders periscope and in front of it a smaller air vent with a recess for the wire mesh grill. If that section of the turret were still present there would also be a hole for the gunners periscope in front of the commander's cupola. In the AC1 neither the gunner nor loader had a periscope leaving them effectively blind to what was going on around outside the tank. The small addition of these two periscopes alone would have made for a far more effective vehicle.
All pictures taken on the 1st of December 2002 at the Melbourne Tank Museum, Narre Warren, Victoria. My thanks to John Belfield for not only collecting these vehicles but displaying them to the public, and Richard Simmie for guiding me through all the bit and pieces.
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