Allied intelligence personnel had deciphered much of the Japanese "Mo" plans through radio intercepts at the Allied Fleet Radio Units (radio intelligence centers) in Melbourne, Australia and Pearl Harbor, Hawaii. Based on this intelligence, on 22 April, U.S. Admiral Chester Nimitz—stationed at Pearl Harbor—directed Allied forces towards the Coral Sea area to interdict the Japanese "Mo" operation. On 27 April, the U.S. aircraft carrier 's Task Force 17 (TF 17), under the command of Vice Admiral Frank Jack Fletcher, sortied from Tonga and was joined by the U.S. carrier 's TF 11 northwest of New Caledonia on 1 May. That same day, Fletcher detached TF 11 to refuel, expecting to rejoin with "Lexington" and her escorts on 4 May at a predetermined location in the Coral Sea.