In the spring of 1941, the Navy was looking to replace its F4F "Wildcat" (also manufactured by Grumman) in light of new developments in the field of aeronautics, and the worsening military situation both in Asia and in Europe. On June 30, 1941 the Navy ordered the prototypes XF6F-1 and XF6F-2. They were to have the Wright R-2600-16 engine, producing 1,700 horsepower, on the -1 and a Wright 2800-16 fitted with a turbo-supercharger on the -2. Immediately after the first flight of the XF6F1 on June 26, 1942, the craft was mysteriously redesignated the "XF6F-3" and the engine was changed to the Pratt-Whitney 2800-10 producing 2,000 horsepower. The reason for the mystery became evident only after the war.
Up until the time of the first flights of the XF6F-1, very little reliable information was available on the Japanese "Zero" fighter (Mitsubishi A6M Zero-Sen) except that it was fast, agile and shot down an alarming number of Allied aircraft. As happened on many occasions during WWII, Lady Luck was about to change all that. At the very time of the first flight of the XF6F-1, a curious incident was occurring 2,500 miles (4,023 km) away on a small island known as "Akutan" in the Aleutian chain….
A Navy PBY, making a routine patrol, happened to pass over tiny Akutan Island and one of the observers aboard happened to notice a dark speck on the tundra below which appeared out of place. The pilot took the "Catalina" down to have a closer look. The speck turned out to be a Japanese aircraft, and even though it was upside down, it was almost immediately identified as a Zero. The radioman sent the coordinates and within hours a Navy recovery team was on the way to investigate. On arrival, the recovery team found the dead pilot, Flight Petty Officer Tadayoshi Koga still hanging in his seat harness. Koga had had engine problems and tried to land the plane on the flat tundra of the small island with the wheels down. The wheels dug in and flipped the Zero on its back, snapping F.P.O. Koga’s neck in the process. The Zero was almost undamaged, even the engine looked to be in good shape aside from a broken oil line.
The Zero was dismantled and shipped directly to the Grumman Aircraft factory in California where it was reassembled and flown. The information gleaned from this fortunate incident put the finishing touches on the Hellcat. It was found the XF6F-1 was marginally slower than the Zero, thus the change from the Wright R-2600 to the Pratt-Whitney Double Wasp R-2800 with an output of 2,000 hp (1,493 kW) for take-off and 1,975 hp (1,474 kW) at 17,000 ft (5,182 m). This engine boosted the Hellcats top speed to 375 mph (604 k/hr), 29 mph (47 k/hr) faster than the Zero. No other unfavorable differences between the two planes could be found and the Hellcat was deemed ready for production. The finalized version of the XF6F-3 was almost identical to the production F6F-3 and Grumman shifted the assembly line into high gear.
In terms of size, the Hellcat was the second largest single engine fighter of the war, being ever-so-slightly smaller than the Republic P-47 "Thunderbolt". At first glance, the F6F appeared too big to operate safely from a carrier. But The Grumman Iron Works had a great deal of expertise in building carrier aircraft. The US Navy wanted a much faster plane carrying heavier loads over far greater distances. The only way to achieve all three goals was the obvious way; design a larger aircraft. There was room for a more powerful engine, room for more armament and for extra fuel.
In order to keep the take-off and landing speeds at a reasonable level, Grumman made the wings proportionally larger than most aircraft (including the Thunderbolt) to reduce wing loading. In fact, the Hellcat had the largest wing area of any single engine fighter of WWII at 334 square feet (31 square meters) as opposed to 300 square feet (27.8 square meters) for the P-47.