M7 Priest 105mm Self-Propelled Howitzer
The M7 self-propelled howitzer motor carriage mounted a 105-mm howitzer which was used for high-angle as well as direct fire. It was the Allies most widely used self-propelled gun. The .50-caliber machine gun is mounted in a raised pulpit-like structure which gave the vehicle the nickname Priest. Even though the M-7 self-propelled 105-mm howitzer was a hastily improvised design that carried inadequate armor, it was a highly effective weapon that combined two superb subsystems: the famous 105-mm howitzer and the rugged chassis of the versatile Sherman tank. The self-propelled gun M7 could climb heights only with difficulty, because of its very significant weight.
The 105mm M1A2 howitzer was mounted on an M3 or M4 tank chassis to create the 105mm Howitzer Motor Carriage M7. The first M7s saw service with U.S. forces in the Philippines in 1941, and they proved particularly effective in British hands against Afrika Korps panzers at El Alamein in 1942. The M7 Priest was a self-propelled howitzer that saw extensive use during World War II as the primary artillery support for armored divisions. The gun got its nickname from the British who said the .50 caliber machine gun ring mount looked like a European church pulpit.
Following World War I, U.S. artillery was seen to be unsatisfactory for modern warfare. Hence, the Army chief of staff set up the Westervelt Board in 1919 which studied existing artillery of British, French, Italian and German designs. The board came up with four important conclusions. Board members said field artillery needed to be:
- motor towed;
- self-propelled;
- capable of 360 degrees traverse.
- able to elevate up to 75 degrees elevation to drop shells into enemy trenches or ammunition dumps on the reverse sides of slopes; and
A lot of this was generated by the idea that in the future, battles would move faster because of motor vehicles, and with greater traverse, artillery could keep up with the speed of the battle. These modifications would improve significantly on existing artillery, such as the 75 mm French gun, that was horse drawn and required additional horses to haul ammunition and spare parts. Also, artillery had to be unlimbered, moved into place and aimed prior to firing. In the early 1930s Army leadership and the Field Artillery School remained leery of motorized artillery.
What the Army had then was senior field artillery officers who were born and raised in the horse-and-buggy era. They were familiar with that, and asking them to go from a horse as a piece of technology to motor vehicles was a huge leap forward. d People then viewed vehicles as smelly and unreliable. Towed artillery gained more acceptance initially, because artillery still arrived at a firing location pulled into place not unlike cannons drawn by horses. Still, towed artillery still necessitated unlimbering, aligning the gun to the target and firing. Also, ammunition wasn't hauled on the weapon.
Military budgets certainly factored in the development of vehicles. With the end of the war, defense spending diminished. Given this fiscal shift, one vehicle could replace a team of six horses to pull an artillery piece not to mention additional horses needed to haul ammunition and spare parts. Also, once artillery was in place, horses still needed to be fed, whereas vehicles could be shut off with no "feeding" required until it moved again.
As the world moved into WWII, self-propelled artillery began to gain acceptance. Speed was of the essence, and a self-propelled gun could be placed and engage the enemy much quicker. Conversely, if need be it could also disengage rapidly and retreat to safer terrain. Either way, self-propelled weapons systems could move more rapidly over rugged terrain and keep up with armor.
At the beginning of the Second World war, it appeared obvious that artillery, advancing on the sweeping wave of the tank and motorized infantry, had to assume a mobility that before that time it had not owned. In the Autumn of 1941 Gen. General Jacob L. Devers, coming from Artillery and then Commander of the newly constituted Armored Force, promoted the adoption of a self-propelled howitzer that could carry out the task of accompanyment of the American attack forces.
At the recommendation of the Board of Officers on the Development of Equipment for Armored Divisions, Secretary of War Henry H. Woodring (1936-1940) directed the Ordnance Department in June 1940 to develop a motorized mount, also called a gun motor carriage, for the 75-mm. gun. The department advocated using commercially-built, high-speed tractors and the 3-inch gun, while the newly created Armored Force wanted self-propelled 105-mm. howitzers. Influenced by the movement towards heavier guns in Europe with the ability to follow the infantry, the Ordnance Department eventually substituted the 105-mm. howitzer for the 75-mm. gun.
Finding a high-speed, light-weight mount was difficult. Driven by expediency, the department experimented with wheeled carriages, half-tracks, and medium tank chassis rather than constructing a mount designed especially for the 105-mm. howitzer. In view of the need for mobility, the Ordnance Department picked a medium tank chassis. It reduced the chassis' armor, dispensed with the closed turret, deliberately rejected incorporating 360-degree traverse because it would increase the weight of the weapon.
The General ordered ordered the construction of two exemplary prototypes of a self-propelled howitzer with a 105mm howitzer mounted on a modified hull of the M3 medium tank under construction for the American Armed Forces. The construction of the two vehicles was commissioned to the Baldwin Locomotives Works. Once they were completed they were sent to the Aberdeen Proving Grounds for the necessary tests.
Development began on the M7 Priest in June 1941, still six months prior to the United States officially entering the war. The first vehicle entered service in the spring of 1942 in the role of providing indirect fire artillery support to armored divisions. It employed a crew of seven: a commander, driver, gunner and four Soldiers to handle ammunition. The 50,000-pound self-propelled howitzer could hit 26 mph on a road or 15 mph cross-country. Fuel efficiency was about 0.67 miles per gallon.
Pilot models were known as the T32 and tests began in January of 1942. After a complete series of tests, carried out in part At Fort Knox, the technical organizations recommended the adoption of the vehicle with a series of modifications. In particular, with the aim of avoiding mount the howitzer in super-elevated position, and consequently in order to reduce the already remarkable shape of the vehicle, it was decided to reduce the maximum angle of elevation of the barrel. That was demonstrated to be an error in the long run, since it forced the artillerymen to improvise in the field firing from a ramp in order to increase the inclination. Other modification demanded the adoption of one mounted antiaircraft machine-gun on a lateral ring. The M7 was equipped, for its close protection, of a small turret located on the before-right of the machine which can mount a .50-caliber machinegun.
The M7 was first developed by combining the lower chassis of an M3 Lee tank with a standard towed 105-mm howitzer. However, the late production M7 or M7B1, was built on the chassis of an M4 Sherman tank. Many points identify it as such: The suspension system and other later tank components such as the single piece differential and final drive housing. The M7 was powered by a Continental 9-cylinder radial engine, and the M7B1 by a Ford tank engine. Without a photo of the rear deck and engine compartment doors it is not possible to determine which of the two a vehicle is.
Once the modifications were adopted the vehicle came standardized in 1942 as the "105 Millimeter Howitzer Motor Carriage M7". Altogether there were 3,490 units produced in various series. In 1942, the Army reorganized the armored division, and the artillery was restructured into three self-contained battalions under the tactical command of an artillery section, still within the division headquarters. Each battalion had three six-howitzer firing batteries, making a total of fifty-four 105-mm. self-propelled howitzers in the division. The M2A1 howitzer was the same as that used in the infantry division but was mounted on an M4 mount (105-mm. howitzer motor carriage M7).
One significant improvement over towed artillery was the Priest's capability to haul its own ammo. Firing a 105 mm cannon with a range of more than 10,400 meters, the Priest could carry 69 shells. Some Priests were converted either to carry a radio, which cut 24 rounds of ammunition, or troop carriers capable of hauling 20 Soldiers plus a commander and driver. The vehicle also had a .50 caliber machine gun. Most did not provide the crew any protection from the elements. Dastrup said some had a canvas cover that could be erected to give some relief from snow or rain.
The M7 series had a motor with a maximum power of 380 HP at 2,400 rpm. It was characterized by the adoption of the components of the M3 medium truck motor, which adopted the Continental R 975 air-cooled radial motor of nine cylinders. At the end of 1943 it was decided to adopt the mechanics of the M4 Sherman tank (equipped with the R 975 C4 motor) and to insert a series of modifications dictated from the experiences from the battlefield. The engineers re-used the frame of the M4 Sherman tank and modified the upper structure of the armored vehicle, by opening a space able to integrate the M2A1 105mm L/22.5 howitzer. In particular, designers added two bulkheads so as to to increase the protection of the crew. The construction of this version was entrusted to American Locomotive Company and, for a small exemplary number, to Federal Machine and Welder Company. A total of 3,490 exemples were built in the period from 1942 to February 1945.
The M7B1 series was substantially similar to the previous type, but it was based on the hull of the wagon Sherman M4A3, propelled by a Ford GAA motor of 8 cylinders in a V [at 60°] and cooled by liquid. This was derived from an aeronautical motor with 12 cylinders. The motor was in a position to distribute 500 HP at 2.600 rpm. This version was constructed in 826 exemples by the Pressed Steel Car Company.
The British were the first to use M7 Priest in combat on the battle fields of North Africa. The Priest first saw action during the Campaign in Tunisia and later in El Alamein.
During the Korean War, with the aim of resolving the annoying problem of the small elevation the howitzer, the M7B2 series was introduced. This was characterized by the raised position of the piece that increased maximum elevation from 35° to 65°. At the same time, in order to make place the howitzer, the emplacement of the antiaircraft machine-gun had to be risen also adding an existing ring to that one.
Although the Priest was used for indirect fire, its maximum elevation to raise the gun barrel only reached 35 degrees. This required crews to position the weapon on inclines to achieve greater elevation to lob shells into enemy positions. The Army normally used four self-propelled Priests per battery, with three firing batteries per battalion. Each gun fired a 100-pound shell either a high explosive steel shell, smoke or illumination rounds. The fires direction center would then call for mass fires all aimed on a particular target. This was termed "area destruction," and the circular error of probability was quite large. Any shell that exploded within a given range was acceptable to ensure taking out a specific target.
About 4,200 Priests were built, and production ended in 1945. The weapons system continued to see action in the Korean War.
After the war the self-propelled M7 was in service in very many allied armies allies. Some were converted into Observation Post ("Priest OP") with the gun removed. They progressively were replaced by the self-propelled M109G. During their service in the some self-propelled ones were equip with a new howitzer of 105mm 34-calliber.
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