M40 155mm Self-Propelled Gun
Gary's Combat Vehicle Reference Guide

TM 9-3305: M40
Country of OriginUSA
RoleArmored combat fire support vehicle
Date Of Introduction1945
Gross Weight41.5 tons (37.6 mt)
Ground Pressure10.4 psi (0.73 kg/cm²)
Length, Overall 30 ft (9.14 m)
Length, Hull 21.75 ft (6.63 m)
Width, Overall 10.33 ft (3.15 m)
Height, Overall 8.5 ft (2.59 m)
Ground Clearance17 in (432 mm)
EngineContinental R-975-C4 460 hp (343 kw) 9-cylinder radial air-cooled gasoline
TransmissionConstant mesh synchronized. 5 speed forward, 1 speed reverse
Range150 miles (241 km)
Fuel Capacity200 gal (757 l)
Road Speed24 mph (39 km/h)
Cross Country Speed?
Swim SpeedN/A
Fording Depth3.0 ft (0.9 m)
Trench Crossing7.7 ft (2.3 m)
Vertical Wall Climb2.8 ft (0.9 m)
Hull front, upper: 0.5 in (12.7 mm)Hull front, lower: 2.5-4 in (63.5-101.6 mm)
Hull sides, below sponson: 1 in (25.4 mm)Hull Sides, above sponson: 0.5 in (12.7 mm)
Hull rear: 0.5 in (12.7 mm).Hull top: 0.5 in (12.7 mm)
Hull bottom, first 36 inches: 1 in (25.4 mm).Hull bottom, remainder: 0.5 in (12.7 mm)
Gun shield: 0.5 in (12.7 mm)
Applique ArmorN/A
Explosive Reactive ArmorN/A
Active Protective SystemN/A
NBC Protection SystemN/A
Smoke EquipmentN/A
Type Mount Typical Ammo Load
155mm M1A1 or M2 Gun M13 (T14) mount 20.
M101 or M101B HE
Additional armament: 8 .30 caliber carbines (with 960 rds ammo), 1 M8 grenade launcher, 12 hand grenades, 12 M9A1 rifle grenades
Fire Control SystemM6 periscope, M12 periscope, M69F telescope, M16A1F (T135) elbow telescope, gunner's M1 quadrant
Main Gun StabilizationN/A
Infrared SearchlightN/A


The 155mm Gun Motor Carriage M40 (T83) was designed to provide highly mobile heavy artillery capable of being put into action in the minimum time.

Principal armament is the 155mm Gun M1A1 or M2 on Mount M13 (T14), a mount consisting essentially of the top carriage, recoil mechanism, and the elevating and traversing mechanisms from the standard field piece. Mounted in the center rear of the vehicle, the gun can be elevated from -5° to +55° and can be traversed 18° left and 18° right. A spade at the rear of the vehicle can be dropped to the ground and imbedded for the purpose of increasing the stability of the vehicle while firing.

This vehicle is based on a chassis that uses components of the M4 medium tank but is wider, lower, longer, and lighter in weight than the M4 chassis. The power train components are standard items used in production models of M4-series medium tanks, as are also the suspensions and tracks. The suspension is of the horizontal volute spring type, with three bogies on each side. The tracks are 23 inches (584 mm) wide and have center guides.

Power is supplied by a Continental R-975-C4 engine through a constant mesh synchronized transmission that provides five speeds forward and one reverse.

The vehicle has stowage for 20 rounds of 155mm ammunition, including propelling charges, primers and fuzes, and for small arms ammunition and grenades.

The differential and final drive housing used is the same as for M4-series tanks, varying from 2 1/2 inches to 4 inches in thickness. Side armor below the fender line is 1-inch and other armor is 1/2-inch. It has, in addition, gun shields of 1/2-inch armor plate.

The M40 has a maximum speed of 24 mph and a cruising range of approximately 150 miles.


"Carriage, Gun Motor, 155 mm, M40 (T83)". Original production model. See data above.


Strongly fortified positions, such as, concrete pillboxes, log and/or earth bunkers or caves fall easy prey to the fire power of the 155mm gun.

The vulnerable points of any of these targets are the many openings present - such as gun ports, doors, or the opening at the mouth of caves. Hits secured through openings detonate inside the strong point and effectively reduce it by killing the personnel and destroying the materiel present.

For attack of this sort, best results are obtained at close range by direct fire. The M40 is particularly suitable for just this type of mission. The mobile mount permits the piece to be brought up into position quickly while the armor protection affords a cover for the gun crew while the point is being reduced.

In all firings with the 155mm gun the normal charge should be used as the use of supercharge will result in the shell rupturing upon impact with extremely resilient targets.

Experience in France in the attack upon German pillboxes indicate that the normal charge will yield satisfactory results. Pillbox walls 7 feet (2.1 m) thick were perforated with a single round.

Against earth bunkers the M101 HE shell with the M78 C.P. Fuze will penetrate 23 feet (7 m) when the normal charge is used. As with concrete the normal charge only should be used in attack on this type of target.