Only 2 or 3 known to still exist.
Hemmi "Sun" Type 98 Maneuvering Slide Rule
Made in Japan by "SUN"
Background: "Type 98" denotes that it was created in AD1938 (Koki or Jimmu Era 2598), which is 1938 in western calendars. The type 98 Movement rule, is a polar coordinate measuring system and was designed to calculate tracking and range data between two moving ships (or objects) to, possibly, provide input to the Type 98 Hoiban and Shagekiban Low Angle Fire Control computer which was specially designed for the Yamato class of battleships (the Yamato and Murushi). It could also have been used as the primary calculator for the smaller guns that were not connected the the electromechanical computers on the main battery of guns. This slide rule could also have been used for Ship-to-Shore or Shore-to-Ship bombardment as well. Another feature of this slide rule is that the Maneuvering Board, with its rotating dial on the slide, can be used to determine course corrections and wind drift. Handy if the battleship Yamato or an aircraft carrier, is to launch an aircraft, it will calculate the best heading into the wind. Submarines, would also use a similar device to calculate intercept vectors. The design of this slide rule mimics the maneuvering board/tables of the Allies, designed in 1920, and is still in use today. The center of the dial is 'My' or 'Own' ship.
Scales and markings translated by Jiro Higuchi. Reference Images used by permission of the Int'l Slide Rule Museum.
Front Scale
Relative Coarse Angle // Speed of My Ship [ Speed of Standard Ship, Distance (Logarithmic Scale) nautical mile/Meters, ] Velocity \\ Velocity Ratio
Back Slide: Time Board, Distance by reading Hour/Nautical Mile or Minutes/Meters
Well: Velocity Ratio =>1, Angle of course alteration, Velocity Ratio =<1
Case: Naugahyde with military division "Air Armament 9/90"
Another of these slide rules was discovered in a bunker, located under a mountain behind the old Taura pyrotechnic factory, which manufactured torpedo's during WWII, and stored them within. The buildings are currently part of the Maritime Self-Defense Force Yokosuka Zosamu depot and Akebono Machinery Co., Ltd. The bunker with its network of tunnels is not open to the public. Search for Yakumo's blog (in Japanese). Google will do a decent translation.