Nakajima Ki-115 Tsurugi
The aircraft's intended purpose was to be used in kamikaze attacks on Allied shipping and the invasion fleet expected to be involved in the invasion of Japan, Operation Downfall, which in the end did not take place.
Because the Japanese High Command thought that Japan did not have enough obsolete aircraft to use for kamikaze attacks, it was decided that huge numbers of cheap, simple suicide planes should be constructed quickly in anticipation of the invasion of Japan.
The aircraft had a top speed of 550 kilometres per hour (340 mph) and could carry a bomb weighing as much as 800 kilograms (1,800 lb), large enough to split a warship in two. However, it was otherwise unarmed, and heavily laden with its bomb, would have been an easy target for enemy fighter aircraft.
The controls were crude, the visibility terrible, and the performance abysmal. Tsurugi had very poor take-off and landing performance and could not be safely flown by anyone other than experienced pilots. There were fatal crashes during testing and training. However new, better versions with improved controls and better visibility were under intensive development. The Japanese High command had plans to construct some 8,000 per month in workshops all across Japan.
The war ended before any flew in combat. Individually, they would have been rather inefficient weapons, but used in waves of hundreds or thousands they could have been quite destructive.