In the early 1950s, SAC's backbone bombers were the Convair B-36 and Boeing B-47 Stratojet. To support this strategy, the SAC 7th Air Division was established in May 1951. At the time, Manston had only partially recovered from the ravages of the Second World War. There were still makeshift bomb shelters, i.e. trenches with tin roofs, and many large circles of lush green grass where Luftwaffe bombs had cratered the runway. The RAF control tower overlooked a bizarre hilltop runway, which was an extraordinary wide and long. The 7th AD expanded Manston by building concrete bunkers suitable for nuclear weapons and upgrading the support facilities for long-term use.