After the Air Force agreed to let Boeing build commercial jets based on the prototype, 367-80, already the basis for the KC-135 military tanker, airlines began to order the 707, the commercial transport variant of the Dash 80. The 707 and the KC-135 had many features in common. Both were visually distinct, with a stinger antenna pointing forward from the top of their vertical fin. The 707's width and 100-foot length made it the largest passenger cabin in the air at the time. Placement of its more than 100 windows allowed airlines to rearrange seats. Location of passenger doors on the left side, at the front and at the rear of the cabin, became standard for subsequent Boeing jets. The exteriors of the 707 and its competitor, the DC-8, were almost identical, but the 707 wing had more sweepback, so it could fly about 20 mph faster.