Both of these fighters were built by Grumman. The F5F's performance was as good as the Grumman F6F Hellcat which wasn't introduced into service until early 1943. Because it wasn't possible to have the single engined Hellcat or Corsair put into service earlier because their engines (Pratt and Whitney R-2800s) weren't available in the 1940-1941 time frame. By the simple measure of putting 2 Wright R-1820s (a very reliable engine) on a new airframe it could have been possible to have Hellcat performance level airplanes being put into squadron service in 1941 instead of the F4F. And a solid Grumman design too. Imagine what tactics Jimmy Thach and his peers would have developed with its superior performance. But the U.S. Navy said no thanks. They preferred the single engine F4F. I would think the biggest drawback with the F5F Skyrocket was the carrier air groups would have had to conduct operations with a smaller number of fighters because the F5F would need more deck space even though the outer wing panels did fold back over the engines. And of course they would require more maintenance hours and parts. Was the higher expense still a big concern after the Fall of France and the Two-Ocean Navy Act? But would the advantages of having a superior and faster fighter than the Zero with better survivability due to its two engines outweigh the disadvantage of having smaller fighter squadrons? Another plus to consider is due to their light weight and high power loading I think the F5F would have been able to operate from the escort carriers with their shorter flight decks and slower speeds. Maybe GM could/should have been building FM Skyrockets in 1943 to 1945. https://en.wikipedia.org/wiki/Grumman_XF5F_Skyrocket https://en.wikipedia.org/wiki/Grumman_F4F_Wildcat So, was this a squandered opportunity for an earlier advantage in the Pacific War or a costly mistake avoided?