By the early 1970s it was apparent that the 400kT warhead of the Pershing Ia effectively precluded use as a tactical missile, since by that time almost all strategic missiles had warheads with lower yields. The new Pershing II was designed with a lower yield warhead and a high-accuracy maneuvering reentry vehicle (MARV) with active radar terminal guidance. In May 1978 flight tests of the new RV on existing Pershing Ia rocket stages began. By that time, however, requirements had changed to countering the Soviet deployment of the SS-20 IRBM system. The range of the Pershing II was more than doubled, to 1600+ km (1000+ miles), and new rocket motors were developed by Hercules, using high-energy fuels and light-weight casings made of Kevlar. By December 1985 all 108 Pershing Ia missiles of the US Army in Europe had been replaced by Pershing II.
The MGM-31C reentry vehicle housed a single variable yield (5-50 kT) W-85 thermonuclear warhead, which was a derivative of the MK-61 Mod 3/4. With its Singer Kearfott inertial guidance system, and the Goodyear Aerospace active radar terminal guidance unit in the warhead, the MGM-31C achieved an accuracy of about 30 m (100 ft) CEP at a range of up to 1770 km (1100 miles).
After the Pershing system was dismantled under the Intermediate Range Nuclear Forces [INF] agreement, the W-85 warheads were modified into MK-61 Mod 11 (B61-11) free-fall bombs.
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