In the late 1930s, the Navy's Bureau of Ordnance developed a tactic to deal with large, heavily defended bomber formations. The fighters would fly above them and drop anti-aircraft bombs. These were small, with a light case containing two pounds of TNT, but would cause considerably more damage than a bullet. BuOrd designed small containers housing two bombs each for installation within the wings, five containers to a side. Twenty bombs were to be dropped at one time, covering an area 150 yards long and 50 yards wide. The pilot was to be provided with a downward vision window for aiming.
This was a requirement in the Navy's 1938 fighter procurement, so the Bell XFL-1 (shown here), Grumman XF5F, and Chance Vought XF4U were all built with the small bomb bays to house the BuOrd containers and a downward vision window. According to a BuOrd history published in 1953: "Although antiaircraft bombs gained a group of staunch advocates, their admirers were more numerous on the higher level of planning than on the lower one of actual combat." The bomb bays were deleted from the production F4U by BuAer although the window remained through at least some (most?) of the F4U-1As. Although BuOrd bought 200,000 anti-aircraft bombs, they were apparently only used as antipersonnel weapons.