Description
TM 9-3140 - 75mm M20 / T21E12 Recoilless Rifles and M1917A2 / M74 Tripod Mounts - October 1957
Item Overview
TM 9-3140 is an October 1957 U.S. Army technical manual for the 75mm M20 and T21E12 recoilless rifles. It also covers the M1917A2 tripod mount and M74 weapon tripod mount. This Cold War publication brings the rifle and its ground support equipment together in one reference for operation and organizational maintenance.
Identification and Features
The listed equipment includes the recoilless rifle family and two tripod designs used to support it in ground service.
- Publication: TM 9-3140.
- Issue date: October 1957.
- Caliber: 75mm.
- Rifles covered: M20 and T21E12.
- Mounts covered: M1917A2 tripod mount and M74 weapon tripod mount.
- Subject: Operation and organizational maintenance.
Function and Manual Contents
This publication addresses the operation, care, and organizational maintenance of the listed rifles and tripods. Organizational maintenance was work assigned to the unit using the equipment. Its combined coverage helps readers study the weapon and mount as a complete system, making it useful for period equipment research and technical reference collections.
Publication History
The October 1957 edition records the Army's postwar support of a weapon developed during World War II. Its formal title retained both the standard M20 name and the earlier T21E12 designation. Army publications continued to cite TM 9-3140 in 1972, linking this edition to a longer record of technical support for the equipment.
Documented End-Item Application
The manual applies to the 75mm M20 and T21E12 rifle family and the M1917A2 and M74 ground mounts named in its title. These tripods supported the crew-served weapon while allowing its direction and elevation to be adjusted. Coverage of the mounting equipment makes the publication relevant to collectors identifying complete rifle displays as well as separate tripod assemblies.
Equipment History
American 75mm recoilless rifle development expanded in 1944 after successful demonstrations of smaller 57mm prototypes. The work progressed through the T21 series, with the M20 standardized in 1945. Its design carried forward principles developed for the M18 recoilless rifle while accommodating a larger projectile. The T21E12 name preserves part of this experimental development history in the manual's title.
M1917A2 Tripod Background
The M1917A2 adapted the M1917A1 .30-caliber machine-gun tripod design for recoilless rifles. It retained the same cradle assembly but used a shorter rear leg. Folding legs could be adjusted separately to suit uneven ground. This shared construction explains the mount's familiar Browning-tripod appearance and its connection to earlier machine-gun support equipment.
M74 Weapon Tripod Background
Army equipment references identified the M74 as the replacement for the interim M1917A2 mount. Its applications included both 57mm and 75mm recoilless rifles, linking it to more than one infantry weapon. The inclusion of both tripod types in TM 9-3140 documents the transition from an adapted machine-gun mount to a later weapon tripod.
Weapon-System Background
The M20 was a breech-loading weapon with a rifled barrel that spun its projectile for stability. Its recoilless design vented propellant gases rearward to balance much of the firing force. This reduced the need for a heavy recoil carriage and helped infantry carry substantial firepower into positions difficult for larger guns to reach. Its main battlefield role was direct fire support against visible ground targets.
History of Use
The 75mm recoilless rifle reached troops near the end of World War II and became a familiar support weapon during the Korean War. Army and Marine Corps units used the M20 against field positions and other ground targets. Surplus 75mm recoilless rifles later found civilian work in avalanche control, supporting Forest Service efforts to protect ski areas and mountain highways. This extended use gives the weapon a history beyond its military role.
Ideal For
This manual suits collections focused on early recoilless weapons, infantry support equipment, and postwar Army technical publications.
- Collectors of M20 and T21-series recoilless rifle references.
- Museums documenting Korean War infantry weapons.
- Researchers studying M1917A2 and M74 tripod development.
- Collectors assembling period rifle and mount displays.
Approx length 6", Approx width 9", Approx height .5", Approx weight 1lbs.
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