SELF-PROPELLED TANK DESTROYER M.18 “HELLCAT”
T49, T67, T70, M18, T41, M39, T9, 765, T86, T87, T88 Type:tank destroyer.
Crew :5 men.
Armament :a 76 mm M1A1 gun; a .50 M2 anti-aircraft machine gun.
Armour:
minimum 7.9mm;
maximum 25.4mm.
Dimensions:
length: 6.65 m
width: 2.87 m;
height: 2.58 m.
Weight in combat order: 17 t.
Ground pressure: 0.84 kg/cm2.
Power to weight: 23.8 bhp.
Engine: Continental R 975-C4 9 cyl. air-cooled gasoline radials, developing 400 hp at 2,400 rpm.
Performance:
road speed: 88 km/h;
road range: 168 km;
straight cut: 1.88 m;
vertical obstacle: 0.91 m;
ford: 1.22 m;
slope: 60%.
Service time: introduced into the US Army in 1944, the first US vehicle using torsion bar type suspension. Withdrawn from service in the United States shortly after World War II but still used in Latin America.
The self-propelled tank destroyer M.18 is representative of an evolution marked in 1942 by the realization of the tank destroyer M.10. He had retained the main armament, a 76.2 mm gun, but was characterized by a clearly modernized hull and a power/mass ratio so favorable that this armored vehicle was the fastest tracked vehicle in the entire Second World War. .
The origins of the M.18 go back to December 1941, when the Ordnance Department recommended the design of a fast tank destroyer armed with a 37 mm gun (the American anti-tank gun of the time) on a Christie suspension chassis, powered by a Wright Continental R.975.
Two prototypes were proposed, the first of which received its homologation around mid-1942 under the acronym T.49. Among the modifications made to the initial specifications, let us note the replacement, in the light of the combats of North Africa, of the gun of 37 mm by a 57 mm, and the adoption of a suspension with torsion bars instead of that Christie type.
The T.49 carried out its trials in July 1942, but the tank destroyer command requested a further increase in caliber and the second prototype received the 75 mm M3 gun from the Sherman.
This resulted in a new design called T.67, with a rounded turret and inclined armor plates, which was considered satisfactory and recommended for adoption. But, as the tests of the new Ml long gun intended for the Sherman had taken place in the meantime, the program was once again modified and a pre-series of six experimental vehicles armed with the new gun was ordered under the name of T.70.
In the end, after a new phase of modifications, bearing in particular on the frontal armor and the change of the turret to counterbalance the gun, the homologation of the Gun Motor Carriage M.18 was immediately followed by a substantial order placed with Buick. It was January 1944 and the entry into service of the Hellcat was hastened.
From February to October 1944, 2,507 M.18s rolled off the line, all destined for the American army.
The technique
The hull of the M.18 deviated from the designs that had prevailed until then, in that its armor did not exceed 13 mm
in thickness even if the plates, welded together, were steeply inclined wherever possible. The tension of the tracks could be adjusted on the move on rough ground by the play of a device connecting the sprocket to the first of the 5 rollers.
The open-air turret was armed with a cannon of 76/55 type M1A1, M1AC or M1A2 depending on the series. This special steel barrel was equipped with a muzzle brake (on the last models), an oblique wedge with automatic operation and firing by firing pin with spring, with electrical or mechanical transmission.
The pilot took his place at the front left, with his second on his right, both having periscopes. The automatic gearbox (Torquematic) had three forward gears and one reverse gear. The three other crew members took their places in the turret; the tank commander seated on the left could use the Browning 12.7 anti-aircraft machine gun mounted on a circular support. The first M.18s were distinguished by the safe provided for the on-board lot, and located on the right of the turret; they were also distinguished by a bulge in the left side of the turret, in place of the usual two chests arranged symmetrically.
Evolution
The Hellcat's gun shell piercing power was 175 mm at 900 m distance, which left no chance for any German tank. However, it was decided to improve it still further by equipping it with the turret of the M.36 automaton tank destroyer, armed with a 90 mm gun.
This operation was facilitated by the fact that, from its conception, the hull of the Sherman had received an oversized circular turret for the 75 mm gun. Thus the Americans did not have to rebuild their entire machine to switch to a higher caliber gun.
In fact, the circular turret of 1.75 m became widespread little by little by equipping in particular, in addition to the Sherman, the heavy tanks M.10 and M.36 and, naturally, the M.18. The turrets were therefore practically interchangeable, which simplified the problem of optimizing the hull/armament couple.
This is how the Super Hellcat was born, armed with the 90 M3 gun, the best US Army Ordnance of All War.
The work was carried out in Aberdeen in June 1945. It was found that the bottom of the turret basket had to be raised by 5 cm to adapt to the lower profile of the M.18, in addition to some minor internal modifications. minor. As for the rest, it was enough to lower the hatches by 5 cm to allow them to open, the piece being in the hunting position. True, the additional 1,360 kg of the new turret was an overload, and the rearward shift of the center of gravity slightly lowered the rear of the hull. Subsequently, it was decided to equip the 90 mm tube with a muzzle brake, because each shot made the machine move back 56 cm! The end of the war came before the homologation of the Super Hellcat, the program of which was then abandoned.
It was the same for the T-.88, a Hellcat armed with a 105/22 howitzer in the turret, very close to the tank destroyer as for the rest. The relative lightness of the M.18 militated in favor of its adaptation to the amphibious role, with a float frame of good configuration and a modest mass. The first prototype of this version, the T.86, was powered by its tracks alone. A second, the T.87 armed with a 105 howitzer, was driven by two propellers 66 cm in diameter. They too arrived too late. Despite good nautical qualities, these models were not without flaws; visibility was poor and it was necessary to fit control surfaces to maintain direction.
The only derivative of the M.18 to enter service was the M.39. A tracked counterpart to the wheeled armored vehicle M.20, named after him the Armored Utility Vehicle, it was born following the suggestion made in June 1944 to use the hull of the M. 18 to make it a troop transport and tow the M6 76 mm anti-tank gun.
Two prototypes were made, the T.41 in the tractor version and the T.41E1 in the reconnaissance machine version. They differed among themselves only in the distribution of loads and the number of seats. The classic Browning C.A. 12.7 machine gun was retained with its circular mount at the forward end of the cockpit.
Approved in early 1945, the M.39 was intended for personnel transport and equipment in the combat zone, as well as the towing of the anti-tank piece mentioned above. In this case, it carried 42 76 mm shells.
The first American fully tracked personnel carrier, the M.39 was also tested as an 81 mm mortar carrier and as a launch tank. -flames (T.65).