Complex sentence: Efficient use of this air in the nozzle was a prime requirement for aircraft that had to cruise efficiently at high supersonic speeds for prolonged periods, hence its use in the SR-71, Concorde and XB-70 Valkerie.
Split into simpler sentences: Efficient use of this air in the nozzle was a prime requirement for aircraft that had to cruise efficiently at high supersonic speeds for prolonged periods. Hence its use in the SR-71, Concorde and XB-70 Valkerie.