Experience gained with 105-mm (4.13- m) howitzers mounted on halftracks enabled the US Army to decide that it would be better if the howitzer was mounted in a fully tracked carriage, and accordingly an M3 medium tank chassis was modified to take such a weapon. The M3 chassis was considerably reworked to provide an open-topped superstructure with the howitzer mounted in its front. The development vehicle was known as the T32, and following trials which added a machine-gun mounting to the right-hand side of the fighting compartment, the vehicle was adopted for service as the Carriage, Motor, 105-mm Howitzer, M7. Maximum armour thickness was 25.4mm (1 in).
The first production examples were for the US Army, but many were soon diverted to the Lend-Lease programme for the Allies, among them the British Army. The British soon named the M7 the Priest, legend having it that the prominent machine-gun mounting gave the impression of a pulpit. The British gunners adopted the M7 with alacrity, and the type first went into action with them at the 2nd Battle of El Alamein in October 1942. The British asked for 5,500 M7s to be produced for their use alone by the end of 1943, but this order was never completed in full. The figure nonetheless provides an indication of the success of the M7 with the British gunners. They appreciated the space and mobility of the carriage and also the extra space for personal stowage. The one snag was the howitzer, which was not a standard British Army type: thus ammunition (stowage was provided for 69 rounds on each vehicle) had to be supplied separately for the M7 batteries, which made for a considerable logistic complication. This was not resolved until the first Sextons with the 25-pdr weapons began to be issued in 1944. Until that time the British M7s were used all through the Italian campaign and some were landed in Normandy in June 1944 though they were soon replaced by Sextons.
The M7 then began a new service career in a revised form: the howitzers were removed and the hulls were used as armoured personnel carriers nicknamed Kangaroos. This soon became a normal fate for unwanted M7s, and the idea soon spread to Italy.
The US Army also made wide use of the M7, although production for the US Army was not a constant process. After 1942 M7 production proceeded in fits and starts. At one stage the original M3 chassis was replaced by the later M4A3 Sherman chassis, and these M7s were known by the designation M7B1.
After 1945 large numbers of M7s were handed over to other countries, and some remain in use to this day in such nations as Brazil and Turkey. The 105-mm howitzer is still a standard weapon all over the world, and thus the M7s continue to fire a 14.97-kg (33-lb) shell to a range of 11430m (12,500yards). Throughout their service life the M7s have always showed outstanding reliability, and have demonstrated their ability to cross all types of rough terrain.
The first M7s produced were modified M3 Lee medium tanks. In order to maintain a low silhouette, the howitzer elevation had to be restricted to 35°. In May 1942, after only a month of production, the vehicle was altered to increase its ammunition storage from 24 to 69 rounds. This was achieved by placing seven rounds on the left wall, five on the right, and storing the remainder under floor plates. The M7 also went through a fairly rapid shift from being based on the M3, to having more commonality with the M4 Sherman. The first major example was an adoption of the M4's three piece housing, single piece casting and suspension. In British service, some M7s carried a radio set, which took the place of 24 rounds of ammunition.
Completing the shift, the M7B1 was fully based on the M4A3 Sherman chassis. It was standardized in September 1943, and declared substitute standard in January 1945.
During the Korean War, the limited elevation of the howitzer became noticeably problematic and it was increased to 65° to increase the effective range of the howitzer. The machine gun mount also had to be raised to give a 360° firing arc.
As one part of the Allied effort to capture Caen and breakout from the Normandy beaches, several M7s had their main gun removed in the field for use as armored personnel carriers and were used in Operation Goodwood. These field modified vehicles were referred to as "Defrocked Priests."
A Canadian armored personnel carrier (APC) conversion of the M7 for use by British and Commonwealth units in northern Europe. The Kangaroo could carry 20 infantry plus a crew of two. A total of 102 were converted between October 1944 and April 1945. The name "Kangaroo" became generic for all APC conversions of armored fighting vehicles no longer suitable for combat, including Ram conversions.
Type: self-propelled howitzer
Weight: 22967 kg (50,634 lb)
Powerplant: one Continental 9- cylinder radial piston engine developing 279.6 kW(375 hp)
Dimensions: length 6.02 m ( 19 ft 9 in); width 2,88 m (9 ft 5.25 in) height 2.54 m (8 ft 4 in)
Performance: maximum speed 41.8 km/h (26 mph); maximum road range 201 km (125 miles); fording 1.219 m (4 ft)
Armament: one 105-mm (4.13-in) howitzer and one 12.7-mm(0.5-in) machine-gun