The story
From Japanese 馬鹿(ばか) (baka, “stupid; foolish”) + bomb. By surface analysis, baka (“stupid; silly”) + bomb, though it pre-dates the borrowing of baka as an independent term from Japanese (which is chiefly associated with Japanese popular culture), and therefore lacks any of the endearing connotations that are now typically associated with it. Coined within the United States Navy during the Pacific Theater of World War II, in reference to the fact that the Ohka had been specifically designed to carry out kamikaze attacks, the belief that these attacks were a counterproductive military strategy for Imperial Japan, and the common assumption that kamikaze pilots were mindless zealots.
Etymology from Wiktionary, CC BY-SA 4.0.