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Mortar, 81mm M1 Muzzle-loading 81mm Mortar (1935)

Authored By Silver Fox | Last Updated: 10/9/2014

The Mortar, 81mm M1, was another French-inspired weapon that went on to see successful combat actions with American forces in World War 2, Korea and Vietnam.

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The American M1 81mm Mortar, like the upcoming M2 60mm Mortar, was based on a French design by Edgar William Brandt (1880-1960). The M1 was a derivative of the French mle 27/31 system (itself an improved form of the Stokes Trench Mortar of World War 1 fame) and slightly altered to suit American needs. The M1 became the standard American battalion mortar of World War 2 and saw action in the Korean War as well as the Vietnam War until it was eventually replaced by the M29 - a lighter 81mm system with a longer reach.

As a weapons engineer, Frenchman Brandt was responsible for a slew of advancements in the field of mortars and projectiles that led to the development of varying 60mm, 81mm and 120mm systems while at the same time furthering HEAT rifle grenade and HEAT-warhead anti-tank weaponry technology. Brandt's designs were heavily copied throughout World War 2 and beyond, making them commonplace throughout the globe in the years following.

The US Army had already garnered experience in the use of the 3" Mk I Stokes Trench Mortar during World War 1. The type stayed in circulation in the post-war US Army though several attempts to find a replacement ultimately came to naught. As a result, the US Army decided to work instead on bettering ammunition. In 1931, the US Army acquired four of the Brandt 81mm prototypes, and, after some slight modifications to suit American use and production methods, the mortar appeared formally as the "81mm Mortar, M1" in Army nomenclature. License production was handled by A.B. Farquhar Company, Pullman-Standard Car Manufacturing and Watervliet Arsenal.

Like the "lighter" M2 system, the M1 was made up of three main components - the firing tube, bipod and baseplate. When completely assembled, the M1 weighed in at 136lbs. Weight was distributed as follows: the tube made up 44.5lbs while the mount was 46.5lbs. The base plate itself was 45lbs. Overall length of the system measured in at 3 feet, 9.5 inches. Muzzle velocity was rated at 700 feet per second out of the smoothbore firing tube. A sustained rate-of-fire of 18 rounds per minute was possible, with the operator loading the M1 by dropping the prepared projectile into the muzzle. A firing pin at the base of the firing tube activated the projectile's primer and ignition cartridge (the projectile was dropped down the tube "fuze-end" first) and the corresponding action launched the round at the predetermined desired angle. The operator(s) need only to protect themselves after the projectile was dropped in the tube. This allowed for an excellent sustained rate-of-fire - a maximum rate-of-fire of 30- to -35 rounds per minute was achievable. The M1 maintained a minimum range of 200 yards and a maximum range of 3,300 yards. Elevation was +40 to +85 with a traverse of 14-degrees. The operator utilized an M4 collimator sight (same as on the M2 60mm derivative) fitted to the bipod for accuracy calculations and adjustments.


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Specifications for the
Mortar, 81mm M1
Muzzle-loading 81mm Mortar


Country of Origin: United States
Manufacturer: A.B. Farquhar Company; Pullman-Standard Car Manufacturing; Watervliet Arsenal - USA
Initial Year of Service: 1935


Overall Length: 944 mm (37.17 in)
Barrel Length: 0.00 mm (0.00 in)
Weight (Empty): 299.83 lb (136.00 kg)


Caliber: 81mm
Action: Muzzle Loading; Primer Impact
Feed: Single-Shot
Muzzle Velocity: 700 ft/sec (213 m/sec)
Rate-of-Fire: 18 rounds per minute
Range: 9,900 ft (3,018 m; 3,300 yds)
Sights: M4 collimater sight


Variants:
Mortar, 81mm M1 - Base Series Designation


T27 "Universal" - Short-lived, shortened form of the M1; never selected for mass production.


Operators:
United States