The Coming Kamikaze Threat in World War II We Never Faced

The USS Callaghan, the last Allied ship sunk by kamikazes.

As the American fleet began to become proficient at meeting the kamikaze threat during the Second World War, night time was usually a period when sailors got a respite from the waves of suicide attackers- the vast majority of kamikaze attacks that took place were during the daylight hours. At night the fleet could repair damage from the day's attacks, sailors could get some rest, and ammunition and supplies for the next day's battles could be stocked. By the time of the invasion of Okinawa in April 1945, the Japanese were already in full swing preparing the Home Islands for the anticipated Allied invasion. Operation Olympic was the code name for the invasion of the southernmost of the Home Islands, Kyushu, and it was scheduled for November 1945. The size of the invasion fleet would dwarf not only what was used at Okinawa, but it would also dwarf the Allied landings at Normandy on D-Day in 1944. Approximately just over 2,700 ships and landing craft participated at Normandy; the invasion of Kyushu would have required over 4,000 ships. In twelve days, over 300,000 American troops came ashore at Normandy; on the beaches of Kyushu during Operation Olympic, it was planned that the same number of American troops would storm ashore in just the first *three* days. Therefore in Japanese defense planning for the defense of Kyushu, called "Ketsu-Go", kamikazes were a key part of disrupting the Pacific Fleet Amphibious Force/Task Force 51. Little known to most, though, is that the planned kamikaze threat would have been of a level of ferocity and technique not widely faced by the US Navy in the Pacific War. 

Through most of the war, the kamikaze threat consisted of primarily front-line aircraft. However, the submarine blockade of Japan made getting strategic materials like the ores used in metal increasingly difficult. Bauxite, for example, is an ore that is the main source of aluminum and the Japanese aircraft industry's main source for bauxite were open pit mines near Singapore. As early as 1943 thoughts began to shift towards the use of wood in new aircraft designs and the Germans had even provided the Japanese with plans for the De Havilland Mosquito, the Royal Air Force's "Wooden Wonder". Mosquito components that had been captured were even shipped to Japan aboard the Imperial Japanese Navy submarine I-29, but it was sunk in July 1944 near Japan. While the Japanese were aware of wood's natural radar defeating properties, any consideration at this point in using wood in aircraft designs was more a practical matter with the ore shortages; any benefits against Allied radars was seen rather remarkably as a secondary and less important benefit. 

Yokosuka K4Y1, probably the type that sank the Callaghan.

By the time the Battle of Okinawa was winding down, "Ketsu-Go" was in full swing on Kyushu and a key part of the defense was the use of massed kamikaze attacks. But the state of Japanese aircraft industry was in disarray with the B-29 attacks and the ongoing ore shortages. In July 1945 to meet the required numbers of kamikaze aircraft, all of the training units were converted to kamikaze units which added thousands of experienced pilots but over 5,000 antiquated biplane trainers made of wood and fabric. But again, at this point in the war, no one in Japan had realized that an elderly biplane trainer was a lot harder to spot on radar- plans at that point were to offset the slow performance of the biplane aircraft by shifting the kamikaze attacks to the night time, the traditional sanctuary period for the American fleet. However, somewhere in the Japanese command structure connected all the dots- on the night of 28 July 1945, the Fletcher-class destroyer USS Callaghan was on radar picket duty off the coast of Okinawa. In a time before the advent of airborne early warning aircraft, radar picket destroyers patrolled the edges of the fleet to search for inbound kamikazes. On this night, an elderly biplane floatplane, most likely a Yokosuka K4Y1 trainer, was warded off on its first pass, but it came around undetected for a second pass and struck the destroyer, sinking it with the loss of 47 sailors. The following night, another elderly biplane struck another radar picket, the USS Cassin Young- though not sunk, 22 sailors were killed and the ship had to withdraw from action for repairs. A third destroyer, the USS Prichett, was aiding the stricken Callaghan, was very nearly sunk by another elderly biplane on a kamikaze mission.

Yokosuka K5Y biplane trainer.

The destroyers had difficulty on downing the attackers for three reasons- it was night, not the usual time kamikazes attacked, secondly, the wood and fabric biplanes were difficult to spot and track on radar, and lastly the wood and fabric construction threw off the proximity fuses of the anti-aircraft guns- the proximity fuse's sensor that triggered the detonation of the round was optimized for metal aircraft; against the old wood and fabric biplanes, the proximity fuzes detonated the round too late, or in some cases, not at all. The action that night against those three radar picket destroyers changed thinking on the role of the 5,000+ elderly biplane aircraft that were going to be used as kamikazes for "Ketsu-Go". Here was an unexpected weapon that could counter the American technological advantages in radar and proximity-fuzed shells fired by anti-aircraft guns. American intelligence analysts had seen the massive change in the air forces of Japan in the summer of 1945 and were well aware of Japanese interests in wood, but it hadn't occurred to the Navy that this was a possibly game-changing combination that would have threatened initial phases of Operation Olympic. It was assumed that fuel shortages would keep most Japanese aircraft grounded and this misconception was reinforced by the increasing lack of air action against the B-29 raids and that US warships even managed to get close enough to the Home Islands to shell coastal targets without getting attacked. In fact, the Japanese had stockpiled fuel just for the use of the kamikazes in "Ketsu-Go". 

Tachikawa Ki-17 trainer aircraft.

At Okinawa, only one of the US Navy's carrier air wings was trained and equipped for night combat, that being Night Air Group 90 embarked aboard the USS Enterprise. By November 1945, only one additional night air group would be available for Operation Olympic, giving only 50 aircraft to defend the invasion fleet at night against well over 5,000 night kamikazes that would have been difficult to spot on radar, using the mountainous terrain of Kyushu to mask their approaches to the invasion fleet, and be of a construction that would probably render a large portion of the proximity-fuzed shells ineffective. 

It is perhaps a blessing that the Japanese surrender following the atomic bombings of Hiroshima and Nagasaki took place. The kamikaze plans for "Ketsu-Go" alone would have well resulted in significant casualties on the shores of Kyushu, but instead history is left with the USS Callaghan as the last Allied ship to be sunk by kamikazes- and that night on 28 July was a small preview of the storm facing the US fleet in the waters of the Home Islands.

Source: Hell to Pay- Operation Downfall and the Invasion of Japan, 1945-1947 by D.M. Giangreco. Naval Institute Press, 2009, p125-137. Photos: Wikipedia.