The P-38 carried their drop tanks between the fuselage and engine. For the mission against Yamamoto only 165 US gallon tanks were available at the squadron, so a supply of 330 gallon tanks were flown in from New Guinea. Each aircraft carried a 165 and a 330 tank. The 330 tank could be carried without any problems, and 2X330 could be carried if required. In this case it was just availability.