Changes

==Prelude==

==Prelude==

Following the outbreak of the Pacific War in December 1941, the Japanese armed forces conducted military operations against U.S., British Commonwealth, and Dutch possessions in the Pacific and Southeast Asia. The first phase of these operations, which was the seizure of Malaysia, Singapore, the Dutch East Indies, the Philippines, and various island groups in the central and western Pacific, was virtually complete by March 1942. The second phase, initiated by Japanese Imperial Headquarters on 23 January, was designed to isolate and neutralize Australia and India. In the Pacific, this plan envisioned the seizure of bases in Papua/New Guinea and the Solomon Islands, which would be used to support future operations against New Caledonia, Fiji, and Samoa. By early March, with the seizure of Lae and Salamaua, the entire north coast of Papua/New Guinea had fallen to Japanese forces who were planning for an amphibious invasion of Port Moresby.

Following the outbreak of the Pacific War in December 1941, the Japanese armed forces conducted military operations against U.S., British Commonwealth, and Dutch possessions in the Pacific and Southeast Asia. The first phase of these operations, which was the seizure of Malaysia, Singapore, the Dutch East Indies, the Philippines, and various island groups in the central and western Pacific, was virtually complete by March 1942. The second phase, initiated by Japanese Imperial Headquarters on January 23, was designed to isolate and neutralize Australia and India. In the Pacific, this plan envisioned the seizure of bases in Papua/New Guinea and the Solomon Islands, which would be used to support future operations against New Caledonia, Fiji, and Samoa. By early March, with the seizure of Lae and Salamaua, the entire north coast of Papua/New Guinea had fallen to Japanese forces who were planning for an amphibious invasion of Port Moresby.

===Early intellegence===

===Early intellegence===

By this time, two secure American naval intelligence centers were in operation in the Pacific: one in Melbourne, Australia, and another at Pearl Harbor ("Hypo"). A third, at Corregidor ("Cast"), was rapidly disintegrating under Japanese air and artillery attacks on the island. Its cryptanalysts and equipment were in the process of evacuation to Melbourne. These facilities intercepted Japanese radio communications and, through traffic analysis and codebreaking, uncovered the location of major fleet units and shore based air forces. More importantly, by translating messages and studying operational patterns, Melbourne and Hypo predicted future Japanese operations. The intelligence centers provided their analysis, through daily communications intelligence (COMINT) briefings and warning reports, to senior American commanders, including Commander in Chief, U.S. Fleet, Admiral [[Ernest J. King]], and Commander in Chief, Pacific Fleet, [[Admiral Chester W. Nimitz]].

By this time, two secure American naval intelligence centers were in operation in the Pacific: one in Melbourne, Australia, and another at Pearl Harbor ("Hypo"). A third, at Corregidor ("Cast"), was rapidly disintegrating under Japanese air and artillery attacks on the island. Its cryptanalysts and equipment were in the process of evacuation to Melbourne. These facilities intercepted Japanese radio communications and, through traffic analysis and codebreaking, uncovered the location of major fleet units and shore based air forces. More importantly, by translating messages and studying operational patterns, Melbourne and Hypo predicted future Japanese operations. The intelligence centers provided their analysis, through daily communications intelligence (COMINT) briefings and warning reports, to senior American commanders, including Commander in Chief, U.S. Fleet, Admiral [[Ernest J. King]], and Commander in Chief, Pacific Fleet, [[Admiral Chester W. Nimitz]].

===AF===

===AF===

In addition to this advance toward Port Moresby, evidence that Japan was intent on expanding east of the Marshall Islands appeared in COMINT in early 1942. Land-based air units and equipment began appearing in message traffic to and from the Marshall Islands and the Mandates. On March 4, the designator "AF" began appearing in partially decoded messages. Then, on March 5 Japanese seaplanes, refueled from a submarine at French Frigate Shoals to the east of Midway, conducted a small armed reconnaissance mission over Oahu. Finally, on March 13, American cryptanalysts got the break they were looking for.  Acting on a hunch that "AF" was Midway, they asked the radiomen there to send an open-air message indicating something was wrong with their water supply; the Japanese sent a message in turn indicating the "problem" with "AF".  The result was both the breaking of the Japanese Navy's General-Purpose Code (JN 25) and the identification of "AF" as Midway Island.

In addition to this advance toward Port Moresby, evidence that Japan was intent on expanding east of the Marshall Islands appeared in COMINT in early 1942. Land-based air units and equipment began appearing in message traffic to and from the Marshall Islands and the Mandates. On March 4, the designator "AF" began appearing in partially decoded messages. Then, on March 5 Japanese seaplanes, refueled from a submarine at French Frigate Shoals to the east of Midway, conducted a small armed reconnaissance mission over Oahu. Finally, on March 13, American cryptanalysts got the break they were looking for.  Acting on a hunch that "AF" was Midway, they asked the radiomen there to send an open-air message indicating something was wrong with their water supply; the Japanese sent a message in turn indicating the "problem" with "AF".  The result was both the breaking of the Japanese Navy's General-Purpose Code (JN 25) and the identification of "AF" as Midway Island.

==Japanese plan==

==Japanese plan==

On April 16, after several months of discussion, Commander in Chief, Combined Fleet, Admiral [[Isoruku Yamamoto]], convinced the Imperial General Staff to agree to his Midway and Aleutians strategy for the summer. In Admiral Yamamoto's view, the capture of Midway Island would allow Japan to pursue its Asian policies behind an impregnable eastern shield of defenses in the Central Pacific. The centerpiece of this plan was a feint toward Alaska followed by an invasion of Midway. When the U.S. Pacific Fleet responded to the landings on Midway, Japanese carrier and battleship task forces, waiting unseen to the west of the Midway strike Force, would fall upon and destroy the unsuspecting Americans. If successful, the plan would effectively eliminate the U.S. Pacific Fleet for at least a year and provide a forward outpost from which ample warning of any future threat by the U.S. would come.

On April 16, after several months of discussion, Commander in Chief, Combined Fleet, Admiral [[Isoruku Yamamoto]], convinced the Imperial General Staff to agree to his Midway and Aleutians strategy for the summer. In Admiral Yamamoto's view, the capture of Midway Island would allow Japan to pursue its Asian policies behind an impregnable eastern shield of defenses in the Central Pacific. The centerpiece of this plan was a feint toward Alaska followed by an invasion of Midway. When the U.S. Pacific Fleet responded to the landings on Midway, Japanese carrier and battleship task forces, waiting unseen to the west of the Midway strike Force, would fall upon and destroy the unsuspecting Americans. If successful, the plan would effectively eliminate the U.S. Pacific Fleet for at least a year and provide a forward outpost from which ample warning of any future threat by the U.S. would come.