The recoilless rifle is a light weight artillery weapon carried by infantry for anti-tank fire or to assault fixed positions. In the U.S. military, the recoilless rifle was first used toward the end of World War II.
Soldier firing a 57mm M18A1 recoilless rifle from the shoulder. 9th Infantry, 2nd Infantry Division in Korea, 5 September 1951.
The recoilless rifle combined a rocket propelled munition with a rifled barrel (unlike the smooth bore bazooka) firing a spin-stabilized round with anti-tank capability. The RR ammunition looks like an artillery round but with "swiss cheese" vent holes in the case allowing escape of the gasses that propel the round. The light recoil made it possible to fire them from the shoulder, a tripod, or smaller vehicles such as a jeep.
There were five major models in the family of Recoilless Rifles fielded by the U.S. Army and Marine Corps:
57mm M18 (WW II & Korea)
75mm M20 (WW II & Korea)
90mm M67 (Vietnam)
105mm M27 (Korea)
106mm M40 (Vietnam)
The M18 and M18A1 recoilless rifle were developed late in World War II for use like a bazooka as an anti-tank or anti-personnel weapon. It was light enough to be fired from the shoulder, although heavier than a bazooka. The M18 takes a 57 mm round effective against 1 inch armor up to a range of 4500 yards (meters) much more range and penetration than the bazooka. The M18 was used by Marines in Okinawa as well as in Korea until replaced by the more effective 3.5 inch M20 bazooka with its HEAT round.
The 75 mm M20 recoilless rifle weighed over 114 pounds and was almost 7 feet long. It was fired from the same tripod used with the M1917A1 .30 machine gun. Its HEAT projectiles were effective against four inches of armor at up to 7000 yards (meters) range, a considerable improvement over the M18 57 mm RR. The M20 was fielded in both the ETO and Pacific Theater during World War II in 1945.
The 90 mm recoilless rifle, M67, was a lightweight, portable, crew-served weapon intended primarily as an antitank or antipersonnel weapon designed to be fired from the ground using the bipod, monopod, or metal frame shoulder stock. Its length was 53 inches (1.35 meters) and it weighed about 37 pounds (17 kg.) Its maximum range was about 2200 yards (meters) but effective in the range 450-800 yards (meters). The M67 was used extensively in Vietnam, especially against bunkers and other fortifications.
106 mm M40 Recoilless Rifle mounted on M-151A1C Weapons Platform in Vietnam. Thanks to Martin Albright for useful suggetions leading to this photo.
The U.S. Army developed a new recoilless rifle, the 105 mm M27, fielded in 1952. The M27 design was unsatisfactory and was replaced with the 106 mm M40 RR by the early sixties. The small difference in bore made it possible to use the M27 ammunition in the M40 (but not the reverse).
The M40A1 and M40A2 recoilless rifles succeeded the M40 and were used extensively by the USMC in Vietnam. Its design included a parallel mouned M-8C .50 cal. spotting rifle. Rounds provided were HEAT, high explosive plastic-tracer (HEP-T), and antipersonnel-tracer (AP-T) (flechette) rounds. It has been used effectively in MOUT operations by U.S. forces in Vietnam, the Dominican Republic, and other areas. Limitations include its long barrel and a major backblast signature and hazard (smoke, dust, flash, and debris after firing).
The 105/106mm RRs were used with tripods, but were quite heavy to be man carried. They were often mounted on specially configured jeeps, starting with the M38A1C jeep, and later on the M151A1C or M-825, followed by the HMMWV.
Ontos ("The Thing") Recoilless Rifle Platform
The M-50 Ontos self-propelled anti-tank artillery, based on a light chassis developed for airborne operations, was mounted with six M40A1 or M40A2 106 mm recoilless rifles. The USMC acquired 176 of them, used for fire support in Vietnam. It was effective but had many drawbacks, including exposing the crew as they dismounted to reload. Ontos was dropped by 1970.
Recoilless Rifles Phased Out and Returned
When wire guided missles became the preferred anti-tank weapon in the U.S. Military after Vietnam, the recoilless rifle was phased out. The U.S. made RRs continue in use in many armies around the world and may make a comeback as light artillery for urban operations. One weapon, the M3 Carl Gustav, has brought the recoilless rifle back into the U.S. arsenal as a weapon for Special Operations.
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