would have been difficult for Allied radar systems of the time to detect and track), they hoped to raise that to one for six by overwhelming the US defenses with large numbers of kamikaze attacks within a period of hours. The Japanese estimated that the planes would sink more than 400 ships; since they were training the pilots to target transports rather than carriers and destroyers, the casualties would be disproportionately greater than at Okinawa. One staff study estimated that the kamikazes could destroy a third to half of the invasion force before landing. Admiral Ernest King, Commander-in-Chief of the U.S Navy, was so concerned about losses from kamikaze attacks that he and other senior naval officers argued for canceling Operation Downfall, and instead continuing the fire-bombing campaign against Japanese cities and the blockade of food and supplies until the Japanese surrendered. However, General George Marshall argued that forcing surrender this way might take several years, if ever. Accordingly, Marshall and United States Secretary of the Navy Frank Knox concluded the Americans would have to invade Japan to end the war, regardless of casualties. Naval forces Despite the shattering damage it had absorbed by this stage of the war, the Imperial Japanese Navy, by then organized under the Navy General Command, was determined to inflict as much damage on the Allies as possible. Remaining major warships numbered four battleships (all damaged), five damaged aircraft carriers, two cruisers, 23 destroyers, and 46 submarines. However, the IJN lacked enough fuel for further sorties by its capital ships, planning instead to use their anti-aircraft firepower to defend naval installations while docked in port. Despite its inability to conduct large-scale fleet operations, the IJN still maintained a fleet of thousands of warplanes and possessed nearly 2 million personnel in the Home Islands, ensuring it a large role in the coming defensive operation. In addition, Japan had about 100 Kōryū-class midget submarines, 300 smaller Kairyū-class midget submarines, 120 Kaiten manned torpedoes, and 2,412 Shin'yō suicide motorboats. Unlike the larger ships, these, together with the destroyers and fleet submarines, were expected to see extensive action defending the shores, with a view to destroying about 60 Allied transports. The Navy trained a unit of frogmen to serve as suicide bombers, the Fukuryu. They were to be armed with contact-fuzed mines, and to dive under landing craft and blow them up. An inventory of mines was anchored to