The B-70 was a high-flying Mach 3 bomber, intended to replace the B-52. It was a canarded delta wing aircraft, designed to 'ride' on the shock wave contained between the lower fuselage and its movable, downturned wingtips. Because of kinetic heating at high speed, the B-70 was built from titanium and steel honeycomb parts. The advent of surface-to-aircraft missiles made the high-flying bomber obsolete. Two were built, as two-seat research aircraft.