Both sides of "PT-59"s highly flammable 3000 gallon gas tanks, housed below decks and immediately behind the cockpit, and the boat’s gunwales were reinforced with armor plate to protect them from return fire. Kennedy was aware that the PT's wooden hulls without armor plating could not withstand even a single bullet or bomb fragment, and that the tiniest shard of hot metal could ignite the gas tanks, instantly destroying the boat and crew. The "59"s crew set up some of the armor for live fire tests and found they could be breached at short range with .30 and .50-caliber machine guns at a frontal angle. On 7 October 1943, the five week redesign of "PT-59" was completed, and on the following day Kennedy was promoted to full lieutenant. A total of five former crewmen of "PT-109" joined Kennedy's crew on "PT-59".