This is a short list so far; please let me know of any others (with sources, please).
- ICHIGO
- operation to capture US air bases in east China
- RO
- air operation to augment the air forces at Rabaul and delay Allied offensives
- SHO
- plan for a counterattack against U.S. forces in the western Pacific. It led to the Battle of Leyte Gulf and failed to prevent a U.S. re-invasion of the Phillipines.
- TOGO
- second phase of the ICHIGO operation
Also, closely related, though not an operational code name per se, the phrase "Climb Mount Nitaka" was used on December 2 1941 by Yamamoto to signal his fleet, then about halfway to Hawaii, to proceed with the attack on Pearl Harbor. Thanks to dem bones for pointing this out. Can anybody provide me with the Japanese original?
Source:
Taken from various publications in the series Report of the Office of the Chief of Military History on the UNITED STATES ARMY IN WORLD WAR II