sentences:  These bombers gave SAC offensive capability in the event of a Soviet first strike, and provided a significant Cold War nuclear deterrent.Beginning in 1961, B-52 bombers also secretly flew as part of the "Hard Head" mission (or "Thule Monitor Missions") over Thule Air Base.The objective of "Hard Head" was to maintain constant visual surveillance of the base's strategically important Ballistic Missile Early Warning System (BMEWS), which provided early warning of Soviet missile launches.