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M7 (Priest) Self-Propelled Gun (1942)

Authored By Dan Alex | Last Updated: 3/8/2010

The M7 Priest received its nickname from the pulpit-style cupola fixture and proved an excellent development of the M3 Lee Medium Tank.

The M7 "Priest" (known formally as the "105mm Howitzer Motor Carriage M7") was the principle mobile artillery system for Allied ground forces throughout World War 2. She was designed to support armored actions in all theaters of the war as her tracked qualities could be put to good use wherever she was needed. Often times giving way to her more popular counterparts like the M4 Sherman, the M7 Priest was no less in value when it came to finding success on the elusive fronts making up the Second World War - her 105mm main gun supplied a much-needed punch to American, British and NATO actions during her tenure. The British fielded their own slightly modified version of the vehicle and the Canadians developed an armored personnel carrier from the base design. Beyond her actions in World War 2, the Priest lived a long and healthy operational life, ultimately seeing extensive combat in the upcoming Korean War (1950-1953). Early M7 Priests were based on the chassis of the M3 General Lee while the chassis of the M4 General Sherman medium tank was soon adopted. By the end of World War 2, the M24 Chaffee Light Tank became the standardized Priest form.

The M7 Need and Its Development

The need for a self-propelled artillery system proved ever apparent since the beginning stages of World War 2. The Germans were quick to acknowledge this need and developed obsolete and even captured systems to fit the bill - usually just mating a powerful field gun or tank-killing weapon to an improvised superstructure atop a proven track-hulled system. Perhaps the only difference between the parties involved was in doctrine - the Germans choosing to field their self-propelled artillery systems in a direct fire role while the Allies generally kept their systems behind the front lines in the indirect fire role.

The US Army itself had already experimented some with the fitting of a 105mm field gun to the existing chassis of their half-tracks but these led to limited successes. What it really needed was a fully-tracked implement utilizing existing components to help facilitate production and keep costs at a minimum while offering unparalleled cross-country performance and fire support for infantry and armor actions during a given operation. The chassis of the M3 Lee Medium Tank was selected as the starting point for it was available in some number and the tracked qualities of her hull offered up the required cross country mobility - a component that would allow the new weapon system to better support the expected armored thrusts across the muddy and hilly European terrain. The upper hull was extensively redrawn and rearranged to make room for the form and function of the M1A2 105mm howitzer.

A pilot vehicle was penciled out under the designation of "T32" and two prototypes were constructed. Self-defense would be handled by a modest addition of a single Browning M2 .50 caliber air-cooled machine gun in a raised cupola. Twenty-four 105mm projectiles would be displaced about the superstructure along the inside of the left and right side walls as well as under the floor, each projectile housed in individual protective cylinders. Armor was 51mm (2-inches) at its thickest point and power was derived from a single Continental R975 C1 series 9-radial engine of 350 horsepower running at 2,400rpm. Suspension was handled a vertical volute spring system. The T32 was placed through an appropriate series of trials at Aberdeen Proving Ground and eventually culminated with the "M7" in February of 1942. Production was slated to begin in April of that year.

M7 Production Begins and Origin of the Priest Name

From April of 1942 to August of 1943, the American Locomotive Company (ALCO) was responsible for construction of 2,814 M7 systems. Via Lend-Lease, 90 of these early examples were shipped to the British 8th Army fighting in Egypt and immediately took on the nickname of "Priest" thanks to the pulpit-like drum-style cupola mounting the .50 caliber machine gun. The British were quick to remove 22 of the 105mm projectiles in favor of installing vital radio communications equipment in their place.

Some revisions were already underway while these early systems were being delivered and this produced three slightly varied forms. Most notable of the revisions was to the ammunition stowage compartments, now increasing hold for up to 69 projectiles of 105mm ammunition.

M7 Priest Walk-Around

Design-wise, the M7 sported a lower hull seemingly identical to the M3 Lee medium tank series. She showcased the same six-wheeled track systems with each mounted to the hull sides in pairs and braced by the suspension system. The drive sprocket was at the front, tied to the transmission system which, itself, was paired to the engine held in a compartment to the rear of the vehicle. The superstructure was a large, fixed formation of slab-sides and seated atop of the hull. The glacis plate was slightly angled and contoured into the forward superstructure facing. The driver was situated to the left of the superstructure and managed the mobility functions of the vehicle. He was afforded a rectangular viewing port that could be left open or closed as actions dictated. The 105mm main gun, and applicable firing system, was situated to his right and offset just right of the vehicle's centerline. As the main gun was seated within the superstructure walls itself, this meant limited side-to-side traverse. To help promote a lower silhouette, the main gun was also originally limited to a 35-degree elevation firing arc. To the right of the main gun mount was the pulpit/observation post usually fitting a single Browning M2 .50 caliber heavy machine gun for anti-infantry/anti-aircraft defense. The superstructure was "open-topped" to help facilitate observation of the battlefield ahead. As such, the crew was unnecessarily exposed to enemy fire, fragmentation effects and the elements. This design element, however, was common practice for such weapon systems during the war. Reported speeds were 24 miles per hour on roads while this degraded to 15 miles per hour off road. Range was approximately 120 miles.

The M7 Priest in World War 2

The M7 received its combat debut under British command in the Second Battle of El Alamein (October 23rd, 1942 - November 5th, 1942) in North Africa against German General Erwin Rommel. Results for the British were, apart from being forced to use the American M1A2 main gun (and therefore American ammunition), excellent subsequently led to an order for several thousand vehicles. However, these were to be shipped sans the American main gun, only to be fitted with British-produced ordnance as soon as delivery ensued. While beneficial to the British Army in the short term, not being able to supply their M7 crews with available British ammunition was something of a logistical problem. Eventually, the M7 was replaced in British Army service by the Canadian-built Sexton (built from the Ram tank, itself a Canadian development of the American M3 Lee) beginning in 1943, armed with the British Ordnance QF 25-pounder main gun straight from the factory. The QF 25-pounder was essentially the British equivalent to the American M1 gun.

Once the British M7s were phased out (either through direct replacement or finding the end of their useful barrel lives), they were utilized as gun-less armored personnel carriers. The Canadians went on to developed these M7s as 20-man, 2-crew conversion armored personnel carriers (APCs) under the generic designation of "Kangaroo" - in some ways becoming a forerunner to today's dedicated armored personnel carriers. Some 102 examples were modified as such from October of 1944 to April of 1945 and used by British and Commonwealth forces, first seeing combat at Caen during the Invasion of France.

Improved Priests

After some months of extended combat use, the M7 was revised for the better. Most important of these changes became the addition of fold-down side and rear armor fixed along the superstructure. As it was, crews of initial M7s were at the mercy of many battlefield dangers no thanks to the low-lying side armor protection of the superstructure. The new side and rear armor fittings improved that drawback to an extent, though crews were still operating in an open-topped fighting compartment. From March to October of 1944, ALCO delivered 500 more of these revised M7s to the US Army. However, there was already a shift undertaken away from the M3 Lee and towards the M4 Sherman chassis - this produced the M7B1 after the base M7 had only been in production for a month.

The M7B1

The M7B1 was quick to come online. This version of the M7 SPG was developed to promote more commonality of parts between the M7 series and the omnipresent M4 Sherman medium tank. The lower hull was built of mild steel plate (pressed steel production) as opposed to armor. Use of the M3 Lee chassis in M7 production soon ebbed away by September of 1943, and the Lee-inspired M7s were fully replaced by January of 1945. The M7B1 specifically used the chassis of the M4A3 Sherman modelas well as the Ford GAA engine. The Pressed Steel Car Company produced 826 M7B1 models which, by late 1943, had become the standard M7 production variant.

The United States Marines in the Pacific oft-times removed the 105mm main gun altogether and used the M7 as a sort of make-shift armored personnel carrier housing thirteen marines. This was apparent in subsequent actions in Okinawa and these M7s became known as "Defrocked Priests". In all, the M7 made up some three American battalions during World War 2 and was reportedly produced in over 4,500 examples (sources vary on the exact total). Ultimately, the system would see action across North Africa, Europe (including Sicily) and throughout the Pacific.

The M37 as a Replacement

The M37 designation (formally as the "M37 105mm Howitzer Motor Carriage") was reserved for "Priests" making use of the M24 Chafee Light Tank chassis, intended to replace the M7 in whole. These tank systems featured an improved working space for the gunnery crew and revisions to the ammunition storage while being powered by twin Cadillac-brand engines. She was armed with an M4 105mm main gun and given 126 projectiles. Of the 448 ordered, only 316 of these were actually delivered. The M37 became the production standard Priest by January of 1945.

Priests in Korea

The M7B2 was developed during the Korean War in an effort to increase the elevation of the main gun for better actions across the mountainous Korean landscape. As such, she had her gun mount and machine gun ring raised, producing a very different sort of frontal appearance. The gun was now able to elevate up to 65-degrees and furthermore increased the range of the main gun. The machine gun ring now had full 360-degree traverse capability to defend all sides of the vehicle from infantry attacks, one of the many dangers afforded to tank crews during the war.

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Specifications for the
M7 (Priest)
Self-Propelled Gun


Country of Origin: United States
Manufacturer: American Locomotive Company; Pressed Steel Car Company - USA
Initial Year of Service: 1942
Production: 4,515


Focus Model: M7 (Priest)
Crew: 7


Overall Length: 19.75ft (6.02m)
Width: 9.42ft (2.87m)
Height: 9.68ft (2.95m)
Weight: 26.0 US Short Tons (23,586kg; 51,998lbs)


Powerplant: 1 x Continental R975C1 9 radial engine generating 350 horsepower @ 2,400rpm.


Maximum Speed: 24mph (39 km/h)
Maximum Range: 120 miles (193 km)


NBC Protection: None
Nightvision: None


Armament:
1 x 105mm M1/M2 howitzer main gun
1 x .50 caliber Browning M2 air-cooled heavy machine gun.


Ammunition:
69 x 105mm projectiles
300 x .50 caliber ammunition


Variants:
T32 - Prototype Vehicle Designation of which two were produced; 105mm main gun mated to chassis of M3 Lee Medium Tank.


M7 HMS - First standardized production vehicle

M7B1 - M4A3 Sherman chassis with Ford GAA engine; pressed-steel construction.

M37 - M24 Chaffee Light Tank chassis; increased ammunition storage; revised fighting compartment; dual Cadillac engines.

"Kangaroo" - Canadian-designed M7 converison models serving as Armored Personnel Carriers.

M7 Priest Observation Post (OP) - Sans howitzer; fittd with radio and special communications equipment.

105mm Howitzer Motor Carriage M7 - Official American Designation.

105mm Self-Propelled Gun, Priest - Official British Designation.


Operators:
United Kingdom; United States; Canada