107mm self-propelled mortar XM106

FIRE SUPPORT VEHICLES

The split circular hatch in the troop compartment roof consisted of a single section opening to the left and a folding double section opening to the right. As on the T257, the 81mm mortar had a 360 degree traverse. When the 4.2 inch mortar was installed, it fired toward the rear with a maximum 90 degree traverse. About this time, the 4.2 inch mortar M30 was designated as the 107mm mortar M30 in line with the policy to convert all weapon calibers from inches to millimeters.

To avoid confusion when armed with the two different weapons, separate designations were assigned to the carrier. When fitted with the 81mm mortar M29, it remained the 81mm self-propelled mortar T257E1.

Using the 107mm mortar M30, it became the 107mm self-propelled mortar XM106. The new system eliminating the T designations had now gone into effect. FMC built three pilots of the T257E1/XM106 and the first was delivered to Aberdeen Proving Ground in May 1961 for engineering tests. The remaining two were shipped to Fort Benning and Fort Knox in July 1961 for service tests.

The introduction of the diesel engine in the M113A1 armored personnel carrier resulted in similar modifications to the mortar carriers. When powered by the power pack from the M113A1, they were designated as the 81mm self-propelled mortar T257E2 and the 107mm self-propelled mortar XM106E1.

In October 1964, the T257E1 was type classified as the 81mm self-propelled mortar M125, Standard В and the T257E2 became the 81mm self-propelled mortar M125A1, Standard A. In a similar manner, the XM106 became the 107mm self-propelled mortar M106, Standard В and the XM106E1 was type classified as the 107mm self-propelled mortar M106A1, Standard A.

The Ml25 and the M125A1 carried 114 rounds of 81mm ammunition. A total of 88 rounds of 107mm ammunition was stowed in the M106 and the M106A1. Both types of mortar carriers were manned by a crew of six including the driver.

Limited production of the XM106 was authorized prior to standardization. A total of 860 M106 vehicles were produced including 589 for United States forces. They were followed by 1,316 M106Als of which 982 were allocated to United States forces. The Ml25 was not released for production, but a total of 2,252 M125Als were completed including 460 for United States forces.

When the M113A2 armored personnel carrier appeared with the improved suspension and engine cooling system, these features also were applied to the mortar carriers and they were designated as the 81mm self-propelled mortar M125A2 and the 107mm self-propelled mortar M106A2. Other features remained the same as on the earlier models.

A turret armed with the Royal Ordnance 120mm breech loading mortar was installed experimentally on an M113A2 in 1987. This carrier was fitted with flotation cells on the sides and a new high displacement trim vane to compensate for the increased weight. The external fuel tanks also were installed.

The M113 and the M113A1 also were adapted as the carrier for the Davy Crockett nuclear weapon. Designated as the Battle Group Atomic Weapon System M29 (XM29) heavy, vehicle mounted, it consisted of the 155mm recoilless gun M64 (XM64E2) with the spotting gun XM77E1 and the recoilless gun tripod mount M121 (XM121). The 155mm recoilless gun was an open breech, single shot, smooth bore, muzzle loaded weapon (U.S. Army).

The 37mm smooth bore spotting gun was mounted coaxially under the M64 gun. The XM388 Davy Crockett projectile was 30 inches long, 11 inches in diameter, and weighed 76 pounds. The yield could be selected up to 250 tons. Obviously too large to fit in the 155mm tube, the projectile was propelled by a launching piston in the recoilless gun. The maximum range was 4,000 meters.

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