As May 6 wore on, the MO striking force ran into troubles on its own, stemming from a mixture of poor intelligence, weak reconnaissance, and terrible weather.

By six o’clock that evening, the Japanese carriers had moved to within ninety miles of RADM Fletcher’s task forces, but neither side knew it.  The two forces wouldn’t begin searching for each other in earnest until early the next morning, May 7, when they first engaged.  Swayed by imprecise intelligence and blinded by the fog of war, both sides continued to make mistakes.

Striking force planes from the Shokaku and Zuikaku made the first one.  Flying to an area where they thought they would find one or more American carriers, they discovered only the U.S. fleet oiler USS Neosho (AO 23) and escort destroyer USS Sims (DD 409), anchored in a remote area where Fletcher thought they would be safe.  The Fifth Carrier Division’s pilots had been misinformed.  Now they were incorrect again, this time misidentifying the USS Neosho as a carrier.  They hit the vessels, sinking the USS Sims and turning the USS Neosho into a floating shell.  The Japanese fliers departed, thinking they had smashed a major portion of the U.S. task force.

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RADM Frank Fletcher (pictured as an VADM)

RADM Fletcher also slipped up.  Scanning the area north of the Louisiades, where he expected to find the striking force carriers, RADM Fletcher’s search planes did indeed spot enemy ships.  Told the previous day that the Zuikaku and Shokaku were north of him, RADM Fletcher assumed his planes had spotted the two fleet carriers – he proceeded to task the USS Lexington (CV 2) and USS Yorktown (CV 5) planes against the ships.  They turned out to be only transports, escorted by the light carrier Shoho.  RADM Fletcher’s aircraft hammered the Shoho, making it the first Japanese carrier sunk by U.S. aircraft. That was fine, but the striking force was still on the loose.

It wasn’t until the following day, May 8 that the main elements of each opposing force located each other and launched all-out strikes.  The two sides were about evenly matched: 121 Japanese planes against 122 American.  Both sides handed out heavy blows, the Fifth Carrier Division sinking the USS Lexington and damaging the USS Yorktown, and the U.S. task force badly damaging the Shokaku and severely depleting the Zuikaku’s aircraft strength.  The encounter forced VADM Inoue to withdraw his armada from the Coral Sea.  Was the fight rally over?  No one was sure, but it certainly was suspended.

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USS LEXINGTON (CV 2)

The Battle of the Coral Sea marked a major milestone in the Pacific War.  It would be the first naval action in which the opposing ships never sighted one another.  It was arguably a tactical success for VADM Inoue, in that his forces destroyed one U.S. fleet carrier while losing only a light carrier.  But it ended up a strategic failure for the Japanese because they were thwarted in their drive to secure Port Moresby, one of their key objectives in the war.

For the first time since Pearl Harbor, a Japanese advance had been turned back, a feat that changed the tone of the Pacific War in one stroke.  ADM Nimitz was satisfied with the outcome and, for the most part, so was ADM King, although he wondered whether Fletcher had been sufficiently aggressive.  ADM Nimitz harbored no such doubts and sought Fletcher’s promotion to Vice Admiral, eventually approved by ADM King.  ADM Nimitz also was pleased with CDR Rochefort and the role played by radio intelligence in the Coral Sea.

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USS YORKTOWN (CV 5)

CDR Rochefort and his analysts, joined by their colleagues at Fleet Radio Melbourne Australia (FRUMEL), early on had pinpointed Port Moresby as the primary objective of the RZP operation.  In their daily reports to CINCPAC and OP-20-G, they had shown the ceaseless buildup of aircraft and carrier strength of the Fourth Fleet at Truk and Rabaul.  In early May they’d established a reasonably accurate timetable for Fourth Fleet movements through the Solomons, around the tip of New Guinea into the Coral Sea, and the projected conquest of Moresby.

Besides their tracking of VADM Inoue’s South Seas force, CDR Rochefort and his team had also provided the Navy’s decision makers with a board picture of the Imperial Navy.  They’d shown its shift back to home waters and it’s positioning for action in any one of several directions.  They had noted its renewed interest in the Aleutians in the northern Pacific and the islands eat of the Solumons, including Palmyre and Hawaii.

Whatever doubts ADM Nimitz nay have retained about CDR Rochefort since their unfortunate first encounter, they were erased by the Battle of the Coral Sea.  COMINT had proved itself.  So had CDR Rochefort and his team of cryptanalysts, traffic analysts, Linguists, and other “crazy” people, as their boss called them.  CDR Rochefort and his crew now enjoyed unprecedented credibility, at least as far as CINCPAC was concerned.  “By this time ADM Nimitz had come to recognize the value and effectiveness of the Intelligence furnished him,” Layton told Lundstrom, “He had become Intelligence conscious and accepted the analysis if intelligence as forming and recognizable picture, and was (perhaps subconsciously) placing more faith in it than he had before.”

CDR Rochefort would put ADM Nimitz’s faith in intelligence to the test in the weeks ahead with the Battle of Midway.  It would be strained at times.  He would have to draw heavily on the trust he had earned during the preceding months.  But ADM Nimitz recognized that CDR Rochefort now saw something new: a building of forces larger than anything seen before.  He didn’t know what it was, but he knew his battered fleet wouldn’t net much rest after Coral Sea – nor would CDR Rochefort’s basement team!

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Captain Ranson Fullenwider led the FRUPAC Radio Intelligence Unit RIU on the aircraft carrier USS Lexington (CV 2) during the Battle of the Coral Sea. He and his team would escape injury when the Lexington was attacked and the ship had to be abandoned. Two months later at the Battle of Midway he would also be leading the RUI team on the USS Yorktown (CV 5) and would be among the last to leave the burning Yorktown with RADM Fletcher.

Source: Elliot Carlson, “Joe Rochefort’s War”