The M141 Bunker Defeat Munition (BDM) is a disposable single-shot, shoulder-fired rocket launcher designed to defeat hardened structures. It is a modification of the United States Marine Corps Mk 153 Shoulder-Launched Multipurpose Assault Weapon (SMAW) and is also called the SMAW-D (where 'D' is for 'Disposable'). It was designed to fill the void in the United States Army inventory of a "bunker buster" weapon. Design The SMAW-D operates on the principle that the recoil created by launching the rocket is counteracted by a "backblast" of gases fired from the rear of the weapon. This makes the SMAW-D inherently dangerous, especially in confined, urban areas, as is with all weapons of this design. The M141 has two configurations: a carry mode in which the launcher is long, and a ready to fire mode in which the launcher is extended to its full length of . The warhead is the same High-explosive, dual-purpose (HEDP) as the USMC SMAW. It is effective against masonry and concrete bunkers and lightly armored vehicles. The projectile can penetrate up to of concrete, of brick, or of sandbags. The warhead is activated by a crush switch in its nose that can distinguish between hard and soft targets. On soft targets, such as sandbags, detonation is delayed until the projectile is buried in the target, producing a devastating effect. On hard targets, detonation occurs immediately on contact. Service history The conferees of the National Defense Authorization Act for Fiscal Year 1994 agreed that the US Army's BDM and the Marine Corps' Short-Range Assault Weapon (SRAW) were too similar to justify separate long-term projects, and that the Army should pursue an interim BDM program. Congress limited BDM procurement to 6,000 units. Two candidates were evaluated for the Army's BDM program. A candidate from McDonnell-Douglas (later Talley Defense Systems) used the same warhead as the Marine Corps SMAW, but with a rocket motor with a shorter burn time. A candidate developed by Sweden's FFV for Alliant Techsystems (later Honeywell) replaced the standard high-explosive anti-tank (HEAT) warhead of the M136 AT4 with the same dual purpose warhead used by the USMC SMAW. FFV designated the bunker buster version of the AT4 as the FFV AT8. In 1996 the McDonnell-Douglas candidate was chosen. In a unique move, the US Army ordered one batch of 1,500 then a second batch of 4,500 which were placed in contingency storage for expedited issue to units