Sexton ( artillery ) The 25pdr SP , tracked , Sexton was a self - propelled artillery vehicle of World War II , based on an American tank hull design , built by Canada for the British Army , and associated Commonwealth forces , and some of the other Allies . It was developed to give the British Army a mobile artillery gun using their Ordnance QF 25 pounder gun - howitzer . From 1943 it replaced the US built M7 Priest ( US 105 mm guns on a M3 Lee tank chassis ) ; these had replaced the British Bishop ( 25 pdr on Valentine tank chassis ) which had been improvised in 1942 . History . In 1942 , the US supplied enough M7 Priest self - propelled howitzer s to equip a number of British Army artillery units in fighting in North Africa . The British found the Priest to be an excellent weapon , which gave artillery the same mobility as tank units . However , the Priest used the American 105 mm howitzer rather than the British equivalent , the QF 25 pounder gun - howitzer . Having to supply different ammunition for a few units complicated supply for the British Army . The US attempted to fit a 25 pounder to the M7 Priest - producing the T51 in mid 1942 - but the program suffered delays including the destruction of the gun mount on the prototype during the first live - firing exercises . US resources were not available for a vehicle solely for British use so Britain turned to Canada . The Canadian Army Engineering Design Branch through the Canadian government ' s Department of Munitions and Supply were asked to build a vehicle similar to the M7 on the Ram tank chassis . The Ram tank was a Canadian tank design that used the chassis of the American Medium Tank M3 as did the Priest . The Ram had been sidelined by a decision to standardize on the Sherman tank for British and Canadian units . A prototype was completed on 23 June 1942 . Following trials in Canada , the Canadian government ordered 124 vehicles in three batches . The prototype was shipped to the United Kingdom in early 1943 , where it underwent further trials ; the vehicle was found to be highly satisfactory and was given the designation " Sexton " ( after the religious custodian ) in May 1943 . The British government ordered 300 Sextons in the summer of 1943 ; however , these Sextons were to be built on Grizzly tank hulls ( Canadian - built M4A1 Sherman tanks ) instead of Ram tank hulls . The Ram - based Sexton was designated as the Sexton Mark I and the Grizzly - based Sexton was designated the Sexton Mark II . British orders for the Sexton II eventually totalled 2 , 026 vehicles . Unlike the Ram , which was inferior operationally to the Sherman and never saw combat as a gun tank , the Sexton was successful . Between 1943 and 1945 , the Montreal Locomotive Works manufactured a total of 2 , 150 Sextons for the use of both Canadian and British forces . The vehicle entered service in September 1943 . The vehicles were first used in combat in Italy by the British Eighth Army . Later Sextons took part in the invasion of France and subsequent Battle of Normandy and the campaign in north - western Europe . During the D - day landings a number of Sextons were ordered to fire from their landing craft as they approached the beaches although the fire did not prove to be very accurate . In spite of its confused origins , the Sexton was a combination of proven parts and proved to be a successful design and remained in British service until 1956 . Unlike Germany , which often used its self - propelled guns ( assault gun s ) in a front line direct fire role , Britain and Canada only used the Sexton for indirect supporting fire . They kept the Sextons well back from the front line and used forward observers to direct overwhelming fire on a target .