The 314 was a response to Pan American's request for a flying boat with unprecedented range capability that could augment the airline's trans-Pacific Martin M-130. Boeing's bid was successful and Pan American signed a contract for six aircraft on 21 July 1936. Boeing engineers adapted the cancelled XB-15's 149 foot (45.5 m) wing, and replaced the original 850 hp (640 kW) Pratt & Whitney Twin Wasp radial engines with the more powerful 1,600 hp (1,194 kW) Wright Twin Cyclone. The Clipper's triple tail was chosen after Boeing tested conventional and twin tails which did not provide enough controllability for safe flight.