The US military attempted - through several notable endeavors - to provide a capable squad-level repeating grenade launcher during the Vietnam War. The most successful of these came to be the M79 of 1961, a brake-action system capable of firing various grenade types though limited to single round fire, requiring manual reloading of the weapon with each successive shot. The XM148 proved another wartime development, this as a prototype 40mm grenade projector with origins in the mid-1960s. It was operationally evaluated during the Vietnam War though never formally adopted into service. The XM148 concept later evolved into the widely-utilized and modern M203 single-shot underslung grenade launcher in circulation today.
The China Lake Naval Air Weapons Station (China Lake Naval Weapons Center) was established during the fighting of World War 2 at China Lake, California under the primary banner of the United States Navy. When the American special forces commitment in Vietnam increased, so too did the requirement for specialized weapon systems - particularly for elements of the Navy SEALs. One such requirement was for a more reliable grenade-launching system that could surpass the capabilities of the existing M79 and prototype XM148 series. Work began in 1967 and fell to the Special Projects Division at China Lake and the new design was attributed to Alfred F. Kermode. Development eventually outputted an interesting end-product, basically recognized as the "China Lake Grenade Launcher" due to a lack of any officially-assigned designation (the launcher was never formally adopted).
The China Lake Grenade Launcher was issued to SEAL units operating in secret operations throughout the Vietnam conflict. It was a repeat-fire, 40mm pump-action grenade projector with combat shotgun-like qualities and a relatively robust design. The external configuration was very much in line with a shotgun in that it sported a solid wooden shoulder stock with integral handgrip, an oblong trigger ring loop large enough for a gloved finger and a squared off, boxy aluminum receiver housing the required internal working components. The frontal section of the weapon exhibited a traditionally-shotgun "over-under" configuration with- the barrel seated at the receiver front and affixed over a tubular magazine lined with a ribbed moving slide. Overall length of weapon measured just over 34 inches with a barrel length of 14 inches. Due to its tubular magazine design, the launcher held the inherent ability to house up to 3 x 40x46mm SR grenades with a forth commonly introduced into the firing chamber. This allowed the operator to maximize his tactical battlefield value and fire off several rounds in repeat fashion before being forced to reload.
The 40x46mm grenade became a primary component of US military operations during the Cold War. It represented a low-velocity development (in contrast to the high-velocity 40x53mm series) and was in wide scale use during the Vietnam War - mainly associated with operators managing the single-shot M79 systems. The China Lake design was unique in its incorporation of a pump-action slide feature feeding from a tubular magazine, the operator needing to managed the slide when introducing fresh grenade rounds into the chamber. A trained and experienced operator could, therefore, fire up to 15 rounds-per-minute and lay down indirect or direct suppression fire against a target or target area at range. Effective range was within 350 meters and muzzle velocity was rated at 250 feet-per-second. Sighting was accomplished through a twin over-weapon installation that incorporated an adjustable rear-mounted square notch sight (75 meters to 400 meters, +/- 25 meter adjustments) and a forward-set folding leaf sight featuring a fixed square notch design.
Production of the China Lake Grenade Launcher was issued in 1968 though fewer than 50 are thought to have been made. It is known that the launcher was utilized by the Navy SEALs during the Vietnam War as well as some elements of US Army special forces (5th Special Forces Group) and the USMC's Marine Force Recon intelligence-gathering detachment. In practice, the weapon proved a sound development though, for whatever reason, never procured in acceptable numbers for standard-issue. The repeat-fire nature of the launcher was a perfect complement to existing special forces hardware. The weapon was also light in the hold weighing some 8lbs when empty and a manageable 10lbs when loaded with a grenade. As such, the weapon could be fielded by an operator already carrying a primary weapon on a looped sling over the shoulder. The American involvement in Vietnam was eventually reduced and, with it, several projects in development or under evaluation were scrapped. The China Lake Grenade Launcher, therefore, did not see widespread acceptance in the years following.
The design did, however, see new life in a 1992 private initiative. In a refined form, the grenade launcher was trialed with promising capabilities though this endeavor fell through by 2009 due to a general lack of interest from major parties in furthering the type. The US military has since adopted the modular German Heckler & Koch M320 40mm single-shot grenade launcher which can be utilized as a standalone weapon (with optics and a collapsible stock) or as an under-weapon accessory and will be replacing the long-running underslung M230 series in full within time. Additionally, the US military is also actively evaluating the South African Milkor MGL multi-shot, repeat-fire 40mm grenade launcher. This weapon has seen combat service in Iraq with US Army forces.