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Deadly suicide attacks by obsolete wooden biplanes threatened to defeat state-of-the-art U.S. radar and gunnery.

The carnage was frightful. During the prolonged April-June 1945 fighting in the invasion and capture of Okinawa – the largest land-sea-air battle of World War II – 400 U.S. warships and large landing craft were slammed by Japanese kamikaze suicide planes or hit during conventional air bombing attacks. Thirty-two American ships were sunk outright. More than 60 of the vessels struck required extensive repairs, and at least 40 more were so badly damaged they were scrapped. Much worse, 4,907 American Sailors were killed and 4,874 wounded. This was by far the most costly naval campaign in U.S. Navy history.

The deadly suicide attacks prompted a flurry of U.S. reactions. Reports, directives and action summaries suggesting countermeasures to the enemy suicide plane menace were circulated from senior commands, and a special “kamikaze” research unit was set up at Casco Bay, Maine, to devise a remedy. Meanwhile, however, suicide attacks suddenly slowed in the wake of the carnage at Okinawa – in fact, all Japanese air activity greatly diminished. This lulled the Americans into assuming that the enemy had run out of both pilots and aviation fuel. Moreover, this assumption was reinforced by the lack of virtually any enemy air response to a series of July 1945 shore bombardments of Japan by American and British battleships – intended to lure large numbers of enemy aircraft to their destruction – leading Chief of Naval Operations Admiral Ernest J. King to boast,“The strong protective screen around the fleet was too much for the fading enemy air strength.” However, this boast proved premature.

Just when the U.S. Pacific Fleet was feeling confident it could handle the developing suicide attack threat, the Japanese succeeded in trading a single, antiquated biplane for an American warship – two nights in a row. First, the night of July 28-29, the destroyer USS Callaghan was hit and sunk with the loss of 47 dead and 73 wounded. The following night, the destroyer USS Cassin Young was struck and knocked out of the war with 22 Sailors killed and 45 wounded. With little radar warning and no visual sighting of the attackers until they were practically upon the ships (despite bright moonlight), the slow-moving wood and fabric biplanes – dubbed “sticks-’n’-string kamikazes” – were the functional equivalent of today’s sophisticated stealth aircraft.

Furthermore, a third destroyer, USS Prichett, was similarly struck while assisting Callaghan. Although two of Prichett’s Sailors were killed and the ship suffered extensive damage, it was able to continue performing its radar picket mission duty of providing early warning of approaching Japanese aircraft to the main U.S. fleet assembled many miles to the south.

Ironically, although the Japanese were well aware that wood absorbed radar waves instead of bouncing them back to a receiver, this “stealth” aspect of a biplane’s material was not the primary factor for why they had for years been keen to reduce the amount of (radar-reflective) metals in their aircraft. Their main reason was scarcity of a strategic war material, namely aluminum. Having broken Japanese codes, U.S. intelligence analysts had long monitored the enemy’s many failed efforts to find a proper substitute for their dwindling stocks of aluminum used in aircraft construction. Wood was the most obvious replacement material; but, although the Japanese had built thousands of trainer planes as well as now-obsolete combat aircraft using wooden frames, the level of craftsmanship in their construction was far below that needed for high-performance aircraft. Even detailed information supplied to the Japanese by their German Axis ally on adhesives, plywood skins and special processes for joining highly stressed parts was of little help.

After Okinawa, however, the Japanese high command had more pressing concerns than aircraft design – the imminence of a U.S. invasion of Japan’s home islands. In expectation of a fall 1945 invasion, the Japan ese devised a simple method for the immediate organization of fully equipped and completely staffed“Special Attack”(kamikaze) formations – they assigned existing training units to the suicide mission. This mid-July mass conversion of training units into combat units not only added thousands of experienced flight instructors, but also 5,400 largely wood and fabric trainer planes plus other outmoded aircraft types containing varying amounts of wooden construction. U.S. intelligence analysts speculated on what the Japanese were up to; but perhaps because they perceived Japan’s interest in wood as related to its perpetual aluminum shortage, the Americans made no connection to the fact that the sputtering antiques were nearly impervious to some of America’s most state-of-the-art technologies – early warning radar and the VT (variable time or “proximity”) anti-aircraft artillery projectile fuze, which used radio waves reflected off a target to detonate the projectile at the optimum distance to achieve maximum explosive impact.  

The Japanese, who throughout the war were slow to grasp the potentials and weaknesses of radar, did not realize how dynamic the “wooden windfall” they had stumbled upon truly was. In fact, the Japanese air staff ’s decision to launch the biplanes in night attacks (when U.S. radar was the only practical means of detecting approaching aircraft) was based solely on the desire to use darkness to mask the biplanes’ lumbering approach, not on any comprehension of their low radar signature “stealth” advantage. Nevertheless, as evidenced by the brilliant successes scored against Callaghan and Cassin Young, the combination of “stealth” wooden biplanes with 2,450 of the 18,600 remaining Japanese pilots qualified for twilight and night missions was a potentially deadly turn of events for the American Sailors, Marines and Soldiers at sea.

Although at the time the Americans did not fully understand the reason for the mass conversion of Japanese air training units into combat units, the successful kamikaze night “stealth” attacks by wood and fabric trainer planes immediately brought the threat into focus. Of particular concern was that one of the most vital defensive weapons in the U.S. naval gunnery arsenal – the proximity fuze – was rendered largely ineffective. Therefore, even when the biplanes could be detected, they were difficult to shoot down. Indeed, since the biplanes did have some metal parts (engines and the bombs they carried), U.S. shipborne radar could eventually “see” the approaching aircraft in time to give the ships’ anti-aircraft guns a few seconds to engage the targets. However, as the U.S. Navy’s official World War II historian Samuel Eliot Morison judged, “proximity fuzes were not effective [against] biplanes of fabric and wood.”

After the war, the U.S. Bureau of Ordnance proudly maintained in its official history that “the Axis was never able to countermeasure the [VT] weapon.” Certainly this is true in terms of active countermeasures; but as historian Morison’s statement reveals, the Japanese had stumbled upon a crude yet effective passive countermeasure.

Fortunately, the war ended before the U.S. Navy was forced to come to grips with this deadly “stealth” threat, but the prominent coverage the topic received within the top secret “Magic” – Far East Summary report demonstrates that the appearance of Japan’s biplanes was already on the front burner as a threat whose urgency would demand action. One action would have been to modify the VT fuze’s transmitted signal to adjust the range from the target that the fuze detonated the antiaircraft round and to manufacture in quantity these modified fuzes solely for use against the slow-moving wooden biplanes (the modified fuzes would not be effective against faster metal aircraft, which would require the use of standard VT fuzes). With 23 American plants manufacturing VT fuzes by this late stage of the war, there is every likelihood that a modified fuze would have been produced in quantity and in time to be distributed to key Pacific Fleet elements by the planned October 1945 Japan invasion, Operation Olympic. And with 12,000 Japanese kamikazes – from wooden biplanes to modern metal aircraft – secretly waiting to swarm the American invasion fleet, the fuzes would have been vital to effective defensive fire.

However, using the modified fuzes effectively in combat would have been extraordinarily difficult. The complexities that this new threat added to both radar detection and fire control would have been enormous as harried Combat Information Center (CIC) personnel scrambled to make instant life-or-death decisions as to whether or not the approaching aircraft was of wooden construction and then rush to orally transfer this absolutely essential firing information to gunnery officers in the anti-aircraft gun turrets. Although the lumbering biplanes would have stood no chance during daylight, a night “stealth” attack – particularly if launched with a mix of slow-moving wooden biplanes and faster modern metal aircraft to confuse CIC personnel – had already proved deadly to U.S. warships and their crews.

The bottom line was that the Pacific Fleet’s CICs were already being overwhelmed during periods of intense combat, and these airsea battles could now be expected to occur not only during the day but also at irregular intervals at night, while simultaneously presenting radar operators with a vastly more complicated environment to deal with. Attacks on Japanese air bases by the Pacific Fleet’s Night Air Group 90, flying from USS Enterprise, had proved their worth; but the mass employment of kamikazes and conventional aircraft would have far outstripped the ability of even two such air groups (the maximum number that could be made available for Operation Olympic) to suppress the hordes. Any efforts by U.S. air elements that dampened down, or completely removed, hostile aircraft from the equation would have saved lives, but every American Sailor understood that it eventually would come down to ship against plane and that the odds that he and his buddies would survive to reach “the Golden Gate in ’48” were not looking good.

Despite the practical employment limitations of a proximity fuze modified to counter the new threat posed by wooden kamikazes, its appearance would have been at least an important morale booster for Pacific Fleet Sailors, and the specially fuzed shells would have indeed knocked down a number of the stealthy Japanese biplanes that otherwise would have killed even more Americans. The sudden and unexpected August 1945 end of the war, however, eliminated the need for modified fuzes as well as the development of special tactics and procedures.

As for the “sticks-’n’-string kamikazes” that made up nearly half of the more than 12,000 Japanese aircraft found hidden away in the home islands after the war – intended to be thrown at American invaders in a blizzard of deadly kamikaze attacks – all but a handful were bulldozed into scrap metal by Navy Seabees and Army engineers by early 1947.


 D.M. Giangreco served for more than 20 years as an editor for “Military Review,” published by the U.S. Army Command and General Staff College. He has written and lectured widely on national security matters and is an award-winning author of numerous articles and 12 books, including “The Soldier From Independence: A Military Biography of Harry Truman” (2009, Zenith Press) and “Hell to Pay: Operation Downfall and the Invasion of Japan, 1945-47” (Naval Institute Press, 2009), from which this article was adapted (see chapters 8 and 12).

Originally published in the March 2013 issue of Armchair General.