G4M Bettys of the Kōkūtai 705), escorted by six navy fighters (Mitsubishi A6M Zero fighters of the Kōkūtai 204), to depart Rabaul at 06:00 and arrive at Balalae at 08:00, Tokyo time. President Franklin D. Roosevelt may have authorized Secretary of the Navy Frank Knox to "get Yamamoto", but no official record of such an order exists and sources disagree whether he did so. Knox essentially let Admiral Chester W. Nimitz make the decision. Nimitz first consulted Admiral William F. Halsey Jr., Commander, South Pacific, and then authorized the mission on April 17. These U.S. commanders judged that the benefits of a successful mission included that Japanese morale would be negatively affected by news of Yamamoto's death and that Yamamoto's replacement would be less capable. When the issue was raised that the mission could reveal that the United States had broken Japanese naval codes, the commanders decided the knowledge could be protected as long as the true source of the intelligence was kept hidden from unauthorized American personnel and the press. Interception To avoid detection by radar and Japanese personnel stationed in the Solomon Islands along a straight-line distance of about between U.S. forces and Bougainville, the mission entailed an over-water flight south and west of the Solomons. This roundabout approach was plotted and measured to be about . The fighters would, therefore, travel 600 miles out to the target and 400 miles back. The 1,000-mile flight, with extra fuel allotted for combat, was beyond the range of the F4F Wildcat and F4U Corsair fighters then available to Navy and Marine squadrons based on Guadalcanal. The mission was instead assigned to the 339th Fighter Squadron, 347th Fighter Group, whose P-38G Lightning aircraft, equipped with drop tanks, were the only American fighters in the Pacific with the range to intercept and engage. 339th Squadron Commander Major John W. Mitchell, already an ace pilot, was chosen to lead the flight. For better navigation, Mitchell asked for a navy compass, which was provided by Marine Corps Lieutenant Colonel Luther S. Moore, and installed in Mitchell's P-38 the day before the attack. All of the P-38 fighters mounted their standard armament of one 20 mm cannon and four .50-caliber (12.7 mm) machine guns, and were equipped to carry two drop tanks under their wings. A limited supply of tanks was flown up from New Guinea, sufficient to provide each Lightning with one large tank