The County class was designed around the GWS1 Seaslug beam riding anti-aircraft missile system. Seaslug was a first-generation surface-to-air missile intended to hit high-flying nuclear-armed bombers and shadowing surveillance aircraft like the Tupolev Tu-16 "Badger" and Tupolev Tu-95 "Bear", which could direct strikes against the British fleet from missile destroyers and cruise missile-armed submarines. The Tu 95 and the improved Tupolev Tu-142 were demanding targets for a missile like Seaslug; the long-range Soviet turboprop aircraft flew at an altitude of , at and were barely within the engagement capability of Seaslug. The improved Mk2 version had 10,000 ft (3000m) greater altitude and speed.