Imperial Japanese Navy Nakajima B5N2 “Kate” Type 97 carrier bomber’s bombing computer.
“This was standard equipment in the cockpit of the Nakajima B5N2 ‘Kate’ carrier attack bomber. This may be one of the few surviving examples of this piece of equipment. Complete and functional, this Type 97 computer uses a Seikosha timer to calculate the dropping of up to six bombs at one of three pre-set intervals. The aircraft commander also served as the bombardier in the B5N and set in the middle of the pilot and rear gunner/radio operator. Time to target would be calculated using an optical sight, then the computer set to run and drop the bombs upon the commander’s flip of a switch on this box – designed to be swiped with a gloved hand. The timer started and the computer-controlled the dropping of the bombs.”
In the first wave at Pearl Harbor, 40 Kates attacked with aerial torpedoes, sinking four battleships (USS California, Oklahoma, West Virginia, and Nevada) while 49 B5N2s attacked with high-level bombs, destroying USS Arizona with a crucial hit.
In the second wave, 54 Kates attacked airfields, each dropping one 534-lb. bomb and either a second 534-lb. bomb or six 133-lb. bombs.