The recoilless rifle became a prominent battlefield anti-tank weapon during the 1950s and 1960s as enemy tank armor (primarily Soviet in nature) became increasingly effective. In the U.S. Army, the recoilless rifle followed the storied Bazooka series of World War 2 (1939-1945) and encompassed such designs as the M67. The recoilless rifle received its name from its action which reduced recoil effects of the exiting projectile by expelling some of the resultant propellant gases out of the rear of a launch tube. Today's best modern interpretation of such a weapon is the Swedish M2 Carl Gustav 84mm. Comparable weapons of the period included the famous Soviet RPG-7.
The M67 was born from design work in the 1960s and entered service in time to see combat action in the Vietnam War (1955-1975). The weapon system was essentially composed of a long, Bazooka-like launch tube with integrated sighting device (telescopic with stadia line rangefinding) and grip-handle trigger area. Due to its "recoilless" design, no complex recoil arrangement was needed which simplified both general operation and serial production of the weapon. A hinged assembly at the rear of the tube allowed access to the breech for reloading. Projectiles were 90mm in caliber was originally intended for anti-armor work but soon found to have value in tackling fortifications. An anti-personnel round also allowed for engagement of dug-in enemy troops at range. A standard M67 operating crew numbered three and a bipod and monopod support pairing was provided along the weapon's length. A heatshield served to protect the primary firer from the heat being generated by the launch tube during firing. Overall system weight was 38 lb with an overall length of 53 inches.
The 90mm projectile was issued as a single-piece munition and its spent shell casing was ejected from the rear of the launch tube after firing. Reloads were dependent upon existing in-the-field stocks. Rate-of-fire was one round-per-minute with five rounds-per-minute made possible under extreme circumstances. Maximum engagement ranges reached 2,300 yards. M371 designated practice projectiles while the M371A1 HEAT was the primary "High-Explosive, Anti-Tank", shaped-charge projectile. M590 served as the anti-infantry flechette round.
Despite its relative effectiveness on the battlefield, the M67 proved a cumbersome weapon being both long and heavy. Three crew had to be committed to the system for efficient function. As such, troopers generally favored their old, improved Bazooka forms (primarily the M20) which were far more portable and achieved similar results against infantry with its 60mm rocket projectile. Additionally, the M67's action resulted in a considerable (and dangerous) amount of back-blast which could end up endangering crewmembers or allied forces nearby. Despite this, the weapon maintained a battlefield role for decades after its adoption. It managed a frontline U.S. military presence into the mid-1970s though many were held in reserve or storage and still operated by specialist forces. From this point on, the M47 "Dragon" and Hughes TOW anti-tank missile systems took over the portable anti-armor role.
Beyond actions in the Vietnam War, the M67 saw use in the Salvadorian Civil War (1979-1992) where the U.S. supported the Salvadorian government. With the U.S.-led invasion of Afghanistan in 2001, the need for a portable anti-fortification/anti-personnel weapon became apparent once more and existing stocks of M67s were brought back in force, serving elements such as the storied 101st Airborne. M67 service continues today (2015) nearly 50 years since introduction of the weapon. Amazingly, as an anti-armor weapon, there is little information regarding its use or effectiveness again enemy tanks.