90th IDPG Weapons


81mm Mortar M1 Background

This article is from TM 9-1904 which is available on this site.

The contents have been supplemented with modern photos and comments or additional information added in some instances.

Date Compiled: 7/17/2007
Editor: Chris Guska

The first attempt to obtain more efficient trench mortar ammunition was with the development of the 75-mm smooth bore mortar in which the old 75-mm French type shell was modified by tapering the shell from the bourrelet back to the base, and fitting an aluminum fin in the base of the shell. The round was propelled by means of an ignition cartridge inserted in a short cartridge case, and with propelling increments inserted between the blades of the fin. The stability of the round was not satisfactory, and the development was abandoned. A streamlined projectile with fin assembly was then designed for the 3-inch trench mortar with poor results. Several attempts were made with shell of different contours, but proved unsatisfactory because proper stability was not obtained.

 After World War I, there was an early trend away from the low powered, muzzle-loading Stokes mortar to breech and rifled mortars which were mounted on wheels. The muzzle velocity, the range, and the weight increased, but in so doing, the effectiveness of the trench mortar was decreased in that it lost its simplicity. The weapon became too cumbersome and unwieldy.

Meanwhile the Edapar Brandt Company worked on the 81-mm trench mortar which turned out to be simple in design, utilizing ammunition which was stable in flight and had a long range. In 1931 and 1932, tests conducted by the War Department proved that this mortar and ammunition were highly satisfactory. In 1932, manufacturing rights were purchased from Brandt Company. The weapon itself was a refinement of the 3-inch trench mortar, consisting mainly of a cross leveling mechanism, a better sight, and a heavier baseplate.  For simplicity and effectiveness, this mortar proved a remarkable weapon

Advantages of 81-mm over 3-inch Trench Mortar Ammunition.
1. The 81-mm ammunition is more stable in flight
2. The 81-mm ammunition has a longer range.
3. The 81-mm ammunition comes to the firing line assembled, ready for use.
4. The 81-mm ammunition utilizes a point detonating fuse.

Types of 81-mm Ammunition: High-explosive shell, chemical shell, practice shell, and training shell.

Class of Ammunition. 81-mm ammunition is classified as semifixed; although the ammunition is designed to be loaded into the weapon in one operation, provisions are made for adjusting the propelling charge at the point of fire.

Description. The ammunition itself is streamline in design. It has a stabilizer assembly in the rear of the shell to produce stability in flight and to seat the propelling charge. The stability adds to the range, velocity, and accuracy of the projectile, and causes the projectile to strike point first, allowing the use of a point detonating fuse. It comes assembled with fuse, propelling charge, and ignition cartridge in place. The only operation necessary before loading the shell into the weapon is to remove the round from its fiber container and then pull the cotter pin or safety wire from the fuse and drop shell into the weapon.



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