The following list represents only a fraction of the numerous code names used during the war. All code names are Allied unless otherwise specified. On a number of occasions, Allied countries and theaters assigned more than one code name to the same plans, events, and conferences. Further complicating the situation were the varying names used for different versions or stages of plans and the existence of codes for operations that were never carried out. Excluded from this list are the personal names, such as Betty, Nell, and Val, given by the Allies to types of Japanese aircraft.
| A-Go | Japanese naval plan to engage the U.S. Fleet east of the Philippine Islands | |
| Alamo | U.S. Sixth Army when functioning as a task force in SWPA | |
| Alsos | Intelligence mission to Europe to determine Axis progress in science and technology, especially the atomic bomb | |
| Anakim | Plan to recapture Burma | |
| Arcadia | First Washington Conference | |
| Argentia | Atlantic Conference | |
| Argonaut | Yalta Conference and the military parts of the Malta Conference | |
| Axiom | Southeast Asia Command mission to military leaders in the United States and United Kingdom | |
| Birdcage | Plan to announce the Japanese surrender to POWs held by Japan | |
| Blacklist | Plan for the postsurrender occupation of Japan | |
| Buccaneer | Plan for an amphibious assault in the Andaman Islands | |
| Cactus | Guadalcanal, Solomon Islands | |
| Cartwheel | Operation conducted by SOP AC and SWPA forces to isolate Japanese-held Rabaul on New Britain | |
| Coronet | Plan to invade the Japanese island of Honshu | |
| Cricket | Malta as a location | |
| Culverin | Plan to capture northern Sumatra | |
| Dixie | U.S. mission to the Chinese Communist headquarters in Yenan, China | |
| Downfall | Plan to invade the Japanese home islands | |
| Dukw | Amphibious 2.5-ton truck | |
| Elkton | Plan to capture New Britain, New Guinea, and New Ireland | |
| End Run | Task force of Merrill’s Marauders in the seizure of Myitkyina, Burma | |
| Eureka | Teheran Conference | |
| Fat Man | Plutonium bomb dropped on Nagasaki, Kyushu, August 9, 1945 | |
| Forager | Plan to capture the Mariana Islands | |
| Galahad | U.S. long-range penetration unit in Burma; also called Merrill’s Marauders | |
| Galvanic | Plan to capture the Gilbert Islands | |
| Iceberg | Plan to invade Okinawa | |
| Ichigo | Massive Japanese offensive in China, 1944-1945 | |
| Ketsu-go | Japanese plan to defend the home islands | |
| Little Boy | Uranium bomb dropped on Hiroshima, Honshu, August 6, 1945 | |
| Magic | Signal intelligence gained from reading high-level Japanese diplomatic messages | |
| Magneto | Yalta as a location | |
| Manhattan Project |
Program to design and construct an atomic weapon | |
| Mastiff | Air supply and rescue of Allied prisoners held by the Japanese, following Japan’s surrender | |
| Matterhorn | Plan for the strategic bombing of Japan by Boeing B-29 planes using Chinese bases | |
| Maud | British committee to study nuclear energy | |
| Milepost | Provision of supplies to the Union of Soviet Socialist Republics for use against Japan when the Soviets entered the war | |
| Oboe | Plan to seize the East Indies | |
| Octagon | Second Quebec Conference | |
| Olympic | Plan to invade the Japanese island of Kyushu | |
| Orange | U.S. contingency plan for a war involving it solely with Japan | |
| Purple | Encoded high-level Japanese diplomatic communications | |
| Quadrant | First Quebec Conference | |
| Rainbow | U.S. contingency plans for wars in which the United States (sometimes with Allies) faced more than one enemy at the same time | |
| RO | Japanese reinforcement of air forces at Rabaul, New Britain | |
| Sextant | First Cairo conference | |
| U.S. SHO | Japanese victory plans to stop the Allied drive in the Pacific | |
| U.S. SHO-1 | Japanese plan to commit most of the Japanese Navy to destroy Allied forces invading the Philippine Islands | |
| U.S. SHO-2 | Japanese plan to protect Formosa and the Ryukyu Islands | |
| U.S. SHO-3 | Japanese plan to defend the southern and central home islands | |
| U.S. SHO-4 | Japanese plan to save the northern home islands and the Kurile Islands | |
| S-l | Section 1 of the U.S. Office of Scientific Research and Development; also used to describe the atomic bomb project | |
| Starvation | Massive mine-laying around Japanese home islands, executed partly by Boeing B-29 bombers | |
| Symbol | Casablanca Conference | |
| Ten-go | Japanese plan to stop an Allied invasion of the Ryukyu Islands and Japan | |
| Terminal | Potsdam Conference | |
| Tradewind | Plan to capture Morotai, Molucca Islands | |
| Trident | Third Washington Conference | |
| Trinity | Test of the atomic bomb near Alamogordo, New Mexico, July 16, 1945 | |
| Tube Alloys | British name for atomic energy research; frequently used in Allied conferences | |
| U-Go | Japanese offensive toward Imphal, India | |
| Ultra | High-level signal intelligence acquired by the Allies | |
| Venona | U.S. operation to decipher intercepted Soviet diplomatic messages | |
| Watchtower | Plan to capture Guadalcanal and Tulagi, Solomon Islands | |
| Zipper | Plan to invade the Malay peninsula |