XM13 / MGM-51 Shillelagh
In the early 1960s, the Army embarked on a three-part tank development program that utilized a radical new concept of a guided, low velocity, 152mm projectile, with a combustible cartridge case. The program included the M551 Sheridan vehicle, a modified M6OAl tank, and the MBT-70 German-American tank program. The concept was based on commonality of ammunition (with the obvious benefits) and a tank killing capability that would "meet the threat" of the 1970s.
The Sheridan is a tank-like weapon system intended to be used as the main reconnaissance item for armor, infantry, and airborne operations and as the main assault weapon for airborne operations, and for combined arms teams not using the heavier Main Battle Tank. The Sheridan's turret contains a 152mm gun-launcher. The 152mm ammunition would include a completely combustible cartridge case and primer which would eliminate hand1ing of expended cartridge cases -- a new weapon concept. The gun-launcher is also capable of firing the Shillelagh missile. The gun-launcher, ammunition, and missile, collectively, are called the Shillelagh Weapon subsystem. The Shillelagh missile is the Sheridan's primary tank defeating round. It provides a greater first-round hit probability, particularly at longer ranges against hard targets, than normally associated with gun-type armament systems.
The missile was equipped with an octal shaped charge. The "shaped charge" was introduced to warfare as an anti-tank device in World War II after its discovery in the late 1930s. The Ballistic Research Laboratory, an ARL predecessor organization, made several important contributions to the development of shaped-charge technology. BRL scientists delineated the penetration mechanics of the stretching, high-velocity jet of metal that is formed by the warhead, thus making it possible to design relatively light, inexpensive weapons to defend against tanks. Guided missiles, such as Shillelagh, TOW, Dragon, and Hellfire, exploited the high penetration capability of such warheads with accurate fire at long range. Further contributions included the demonstration of tandem shaped-charge warheads and the application of advanced liner material technology that increased jet velocity and ductility and provided enhanced lethality within existing weapon system envelopes.
On November 4, 1969, the Senate and House Armed Services Committees Conference Report directed the Army to re-evaluate the Shillelagh and TOW missiles with an eye toward substituting the Shillelagh for the TOW in order to meet the Army's requirement for an antitank weapon for both the helicopter and infantry. The re-evaluation for the infantry application, completed in March 1970, addressed the cost, schedules, and operational effectiveness of the two systems. The findings were that the substitution of Shillelagh for TOW would delay the fielding of an acceptable heavy antitank-assault weapon for at least four years, result in no dollar savings, be less satisfactory from an operational viewpoint, and introduce the inherent risk of any development program. (Shillelagh was designed to be fired from a closed breech in an armored vehicle; in infantry and helicopter roles, an open breech launcher and miniaturized guidance and control components would have to be developed and tested.) The Army therefore recommended to the Congress that the TOW program be continued and that no further consideration be given to Shillelagh as a basic heavy infantry weapon. As the fiscal year closed, the re-evaluation of the Shillelagh and TOW missiles as helicopter-borne armament remained under study.
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