Description
TM 9-3140-34 - 75mm M20 / T21E12 Recoilless Rifles and .30-Caliber M7 Subcaliber Rifle - October 1957
Item Overview
TM 9-3140-34 is a field maintenance technical manual for the 75mm M20 and T21E12 recoilless rifles and the .30-caliber M7 subcaliber rifle. This October 1957 copy documents Army maintenance support for both the full-size infantry weapon and its reusable training device. It adds useful technical context to a collection of early recoilless rifle equipment.
Identification and Features
The two calibers identify the service weapon and the smaller training rifle used with it.
- Publication: TM 9-3140-34.
- Date: October 1957.
- 75mm rifles covered: M20 and T21E12.
- Subcaliber equipment covered: .30-caliber M7 rifle.
- Subject: Field maintenance.
- Historical setting: Post-Korean War and early Cold War equipment support.
Function and Manual Contents
The contents address equipment descriptions, model differences, maintenance parts, tools, and inspection. Inspection subjects include the barrel and chamber, breech mechanism, and rifle functioning. The manual also covers inspection before overseas shipment, ordnance shop inspection, and troubleshooting, placing it within the Army's specialist maintenance reference library.
Publication History
The 1957 volume carried forward field maintenance material from TM 9-314, dated April 8, 1949, and related guidance in TB ORD 555, dated March 12, 1954. Its coverage reflects the Army's continued support of wartime recoilless weapons after the Korean War. Including the M7 also documents the maintenance needs of the training equipment used alongside those weapons.
Documented End-Item Application
The M7 subcaliber rifle was designed for training with the 75mm M20 or T21E12 recoilless rifle. It used the sighting equipment issued with the parent weapon. This relationship explains why the manual covers both 75mm and .30-caliber equipment as parts of the same weapon and training system.
Equipment History
American 75mm recoilless rifle development expanded in 1944 after successful demonstrations of smaller 57mm prototypes. The work progressed through the T21 series to the M20, standardized in 1945. The larger weapon carried forward design principles developed for the M18 while giving infantry a heavier projectile. The T21E12 designation in the manual preserves part of that development history.
M7 Subcaliber Rifle Background
The M7 was a reusable training rifle built in the shape of a 75mm cartridge. Its cartridge-shaped body contained a .30-caliber barrel, allowing crews to practice with small-arms ammunition while using the parent rifle's sights. The device also supported loading practice. Its design combined the handling of larger ammunition with a smaller training projectile.
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 move substantial firepower into positions difficult for larger guns to reach. Its battlefield role centered on direct fire against visible ground targets.
History of Use
The 75mm recoilless rifle reached troops near the end of World War II and saw extensive use during the Korean War. The M20 served as an infantry support weapon against field positions and other ground targets. The M7 supported crew instruction with smaller ammunition and repeated handling practice. Army ammunition references still described the M7 in 1967, documenting its place in Cold War training equipment.
Ideal For
This manual suits collections that connect military weapons with the equipment used to maintain them and train their crews.
- Collectors of M20 and T21-series recoilless rifle references.
- Researchers studying the M7 subcaliber training rifle.
- Museums documenting Korean War and Cold War infantry equipment.
- Military technical libraries focused on field maintenance publications.
Approx length 6", Approx width 9", Approx height .2", Approx weight .4lbs.
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