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M21 rocket launcher, 4.5 inch, 25-tube, Trailer Mount

M21 rocket launcher, 4.5 inch, 25-tube, trailer mount (T123 during development), Fort Polk Military Museum outdoor park, Ft. Polk, LA, 31 March 1983
M21 rocket launcher, 4.5 inch, 25-tube, trailer mount (T123 during development), Fort Polk Military Museum outdoor park, Ft. Polk, LA, 31 March 1983.

The M-21 rocket launcher is used to launch smoke rockets and high-explosive rockets against ground targets, electrically firing its five rows of five rockets each. It has limited accuracy so it is used against area targets where dispersion of rockets is desirable. It was derived from the WW II T-66 rocket launcher which had three rows of eight tubes each. Approximately 1200 of the M21 rocket launchers were produced at Rock Island Arsenal, fielded starting in 1953. During development, the M-21 was known as the T-123.

The M-21 4.5-inch multiple rocket launcher is a multiple rocket launcher having 25 tubes or stations. The carriage is a two-wheeled solid wish-bone trail type carriage with pneumatic tires and hand-operated parking brakes. A 1/4-ton 4x4 vehicle (jeep) is used for traveling, and a 2 1/2-ton vehicle is provided for ground transport of smmunition.

The rocket cluster is balanced in trunnions in the trail without mechanical equilibration. Elevating and traversing handwheels and the sight for direct and indirect fire are grouped at the left side of the carriage for one-man control. Elevation of the cluster is accomplished through operation of a worm and worm wheel type elevating mechanism and an elevating arc on the cluster. Traversing is accomplished by handwheel operation which moves the trail on the carriage axle. Elevating and traversing handwheel brakes prevent a change in position of the cluster during firing.

Rockets are muzzle-loaded in the cluster and are electrically fired by single rounds in a preset sequence. The rate of fire is limited only by the operator's speed in operation of the firing mechanism switch. The firing mechanism located in the control box contains a lanyard-operated magneto. To prevent side deflection of the carriage when firing with the lanyard-operated firing switch, wheel stakes are provided to be driven in the ground at each carriage wheel. The spade and trail stake prevents movement of the trail during firing.

The M21 rocket launcher weighed 3,366 pounds (1530kg). Its overall dimensions were 179-in long, 57 5/8-in high, and 79 1/2-in wide when in travelling position.

Technical Manual: TM 9-392A (T123) October 1951.