The development of the M5 light tank followed the realisation that the demands of US tank production might exceed the number of radial aircraft engines that had been the preferred power plants for US tanks. The tender for new engines emphasised using engines already in production.
In June 1941, Ordnance authorised the installation of two Cadillac automobile engines with their Hydromantic automatic transmissions in an M3 light tank. The M3E2 light tank pilot passed a 2000 mile (3219 km) endurance test at the General Motors Proving Ground. Though 2500 lbs (1134 kg) heavier than an M3A1 light tank, the M3E2 had the same performance and better operating characteristics – better coldweather starting, quieter running and reduced workload for the driver because of the automatic transmission. Using a standard automobile engine also eased spare parts and maintenance concerns.
ORIGINS OF THE M5 LIGHT TANK
Initially the M3E2 with the new power train was designated as the M4 light tank. The desire for an improved hull led to the M3A1E1 project, but in fact that was dropped and the M3E2 pilot model was rebuilt with a welded homogeneous armour upper hull similar to that later developed for the M3A3 light tank, resulting in the M3E3.
The new upper hull for the M3E3 had a sloping glacis plate moved forward which allowed room for two hatches in the forward hull roof for the diver and assistant driver. Both hatches had rotating periscopes fitted, and direct forward vision was through a pair of 2-inch (5cm) holes in the glacis plugged with removable plugs pushed out from inside and retained by chains. The new upper hull had more interior room for the driver and assistant driver. The hull sides were vertical.
This early production M5 light tank was seen at Camp Chorrera in Panama in March 1943. It showed the more spacious improved hull combined with the turret of the M3A1 light tank. Note the vision ports in the turret, the sign of very early production M5 light tanks.
A .30 M1919A4 light machine gun was set in a ball mount for the assistant driver on the right side (off-side) of the glacis and initially a fixed .30 M1919A4 was provided for the driver to operate, aiming by steering the entire vehicle as on the M3 light tank. Both the driver and assistant driver had steering and control pedals for driving the M3E3 light tank.
The installation of the two Cadillac engines required the rear deck to be raised to clear the cooling system. The Cadillac engines and transmissions also required lengthening the lower rear hull, the rear idler and mount being moved to the rear, slightly increasing the length of the track.
The M3E3 retained the turret of the M3A1 light tank fitted with power traverse and a gyrostabiliser for the 37mm M6 gun. Because the drive shafts were much lower, there was considerably more room inside the fighting compartment below the turret basket, allowing most of these components to be installed there. The M23 gunner’s sight was coupled to an M4 periscopic sight on the turret roof and a cover sealed the hole for a telescopic sight in the mantlet.
The 14th Armored Division trained at Camp Chaffee where these M3A1 and M5 light tanks were seen in 1943. The new hull of the M5 had better ballistic protection over the M3 and M3A1 and also provided the driver and assistant driver with their own roof hatches.
The 2nd Armored Division trained at Camp Forrest in 1942. This M5 light tank was seen on a road march in the distinctive training markings of the division at Camp Forrest. This was one of the first two full armoured divisions created in the new U.S. Armored Force.
“QUEEN LOIS”, an M5 light tank of the 2nd Armored Division, was seen during a training exercise at Camp Forrest. The raised area on the rear deck accommodated the new Buick automotive engines. The M3A1 scout car was assigned to the unit intelligence officer.