WW2 Japanese Navy Pilot 天測平均盤 Nighttime Astronomical Average Calculator Board Oct 1943

This a WW2 Japanese Navy Pilot’s “Celestial Average Computer” used to aid pilot’s navigating by the stars at NIGHT.

This is designed to slip into one of the many pockets on a Japanese aviator’s flight suit.

It is marked on the dataplate 天測平均盤 “Celestial Average Computer.”

The dataplate has a NAVY anchor mark and a 10th Month of Showa 18 (October 1943) date of manufacture.

The dataplate inducates it was made by 合名會社測機舍 which is the Sokkisha Partnetship. This company made surveying equipment before the war. They became a prime contractor for the various navigation and bombing instruments carried by pilots and crew.

This handheld instrument was carried in the cockpit by night flight qualified pilots as well as in the fuselage of bombers.  Without it, a pilot would likely end up in the sea.

There is a peep hole on the outer edge to align with a particular star or constellation.

• • Doctrine and Training: Early in the war, the IJN trained extensively for night naval combat, including torpedo bomber raids and land-based attacks. They screened new recruits for exceptional night vision to leverage human capabilities over equipment they lacked.

• Technological Limitations: The Japanese air forces largely lacked effective airborne radar, a critical technology used by Allied night fighters (such as the American P-61 Black Widow and radar-equipped F6F Hellcats) to find targets in the dark. Japanese night attacks often relied on visual spotting, illumination flares, or guidance from ground/ship-based lookouts.

• Pilot Attrition: As the war progressed, Japan suffered heavy losses of its highly trained veteran pilots. Replacements received minimal training, making complex, dangerous night operations even less feasible for the majority of new pilots.

• Focus: The vast majority of air operations, including the later-war kamikaze attacks, were conducted during daylight hours, often at dawn or dusk, to maximize the (limited) chances of reaching their targets visually.