The M1 could utilize a variety of ammunition types beginning with the M43A1 Light HE (High-Explosive) round. The 6.87lb M43A1 maintained a fragmentation radius of 25 yards and featured a surface detonating fuze. The 10.6lb M45 and M45B1 Heavy HE rounds greater explosive punch at the expense of range (2,558 yards), this working from a delayed fuze. The 15lb M56 was another Heavy HE round of even greater explosive firepower with a more limited range of 1,300 yards. The fuze on these particular projectiles was adjustable as needed. Shells were stabilized along their flight path via fixed fins at their rear sections to compensate for the M1's use of a smoothbore firing tube (i.e. no rifling for inherent course trajectory).
Besides the conventional explosive rounds, the M1 could also make use of the 10.7lb M57 FS white smoke round out to 2,470 yards or the 10.74lb M57 WP (White Phosphorous), this also ranged out to 2,470 yards. The White phosphorous round was also equally adept at attacking infantry as an incendiary munition. The M301 was a useful illuminating round with an adjustable fuse and 60-second burn duration and deployable parachute, the latter helping to retard the projectile's fall.
Transport of the heavy M1 was solved through the use of a two-man hand cart designated simply as the "Hand Cart M6A1". This allowed the least possible amount of crew to move the mortar system about, allowing transport of the weapon into defensive or offensive positions as required with relatively little pain. Another option was to have the system towed via mule by way of a specially-devised harness. Despite its inherent weight drawback of the M1 kit, the firepower of the mortar offset any negatives especially when supporting artillery would not be made available in a given operation. A well-trained and experienced mortar team could engage targets in defilade, trenches, ravines or on slopes and, as such, proved lethal against enemies in both the European and Pacific theaters of war.
For another method of transportation, the M1 could most effectively be driven around on the back of an M3 Halftrack. These half-tank/half-truck "mutt" vehicles held the inglorious task of transporting just about anything under the wartime sky. From the rear of the M3, the M1 could be fired without the need for the crew and weapon to disembark from the vehicle, affording a certain level of "hit-and-run" tactical advantage. At any rate, this method of fielding the M1 proved most useful to any company commander.
A shortened version of the M1 was unveiled as the T27 "Universal" but this only appeared in limited numbers and was never ordered for mass production. A special tube extension system was also devised for the base M1, though this was hardly used in practice.
The M1 81mm Mortar was complimented in the field by the lighter M2 60mm Mortar beginning in 1940. The M2 was a more "portable" device that allowed for efficient close-support indirect fire and could operate closer to the actions of frontline infantry, its portability being a major plus.
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