'Kikusai (i) was the Japanese navy kamikaze aircraft campaign against the US naval forces off Okinawa during the 'Iceberg' invasion and conquest of that island (6 April/22 June 1945).

At the time of 'Iceberg', the Japanese navy had available some 2,000 aircraft capable of reaching the island (300 in Vice Admiral Takjiro Onishi’s 1^st Air Fleet on Formosa, 800 in Vice Admiral Kinpei Teraoka’s 3^rd Air Fleet around Tokyo on Honshu, 600 in Vice Admiral Matome Ugaki’s 5^th Air Fleet on Kyushu, and 400 in Vice Admiral Minoru Maeda’s 10^th Air Fleet on Honshu), despite the preparatory strikes by US carrierborne aircraft which had inflicted great damage on Japanese airfields at aircraft in the area.

The Japanese were aware that 'Iceberg' was about to start, and decided on a pre-emptive attack against the US fleet base at Ulithi with 24 explosives-laden Yokosuka P1Y aircraft guided by four flying boats. However, this raid was recalled when erroneous intelligence suggested that there was only one US aircraft carrier at Ulithi, whereas there were in fact eight. On the next day another attempt was made, but only 11 aircraft reached Ulithi, one bomber causing damage to the fleet carrier Randolph.

Some 50 kamikaze aircraft were launched against the carrier forces decimating Japanese air strength between 18 and 20 March, and scored a crippling hit on the fleet carrier Franklin and lesser hits on the fleet carriers Essex, Wasp and Enterprise. And so the campaign continued, with small- and large-scale kamikaze attacks whenever the Japanese could find targets. The first raid using the special Yokosuka MXY7 Ohka suicide aeroplane was made on 21 March, and showed the type’s basic vulnerability while being carried by the unmanoeuvrable Mitsubishi G4M 'Betty' bomber conversion. The only successful sortie by the Okha was on 12 April, when two out of 12 scored hits, sinking one destroyer and damaging another. These destroyers were on picket duty well clear of the main US naval forces, a ring of such ships being able to provide the radar coverage that gave the defending fighters time to intercept and the major warships time to organise their truly formidable anti-aircraft defences.

Experienced US naval officers were generally of the opinion that it took the Japanese about four days from the day of a landing to organise any major air counterattack, but poor weather on 5 April gave the Americans a 24-hour reprieve, and thus it was 6 April which saw the beginning of the largest and costliest kamikaze attack of the war, the first of the 10 Kikusui attacks launched as part of Ten. While Toyoda was unable to concentrate the 4,500 aircraft he had hoped to deploy against the US and allied invasion fleet, he was able to muster 699 aircraft, including 355 kamikaze machines, on 6 and 7 April.

Some 182 of these aircraft broke through the US defences to attack the invasion force. These succeeded in sinking three destroyers, two cargo ships, a landing ship and two minecraft, wrecking beyond repair another three destroyers and a destroyer escort, and knocking the battleship Maryland, two destroyers, one transport vessel and one minecraft out of the campaign; another six warships were badly damaged. The total of casualties on the sunk or damaged ships was 485 men killed and 582 wounded. The US combat air patrol claimed 310 Japanese aircraft shot down, and another 41 were claimed by anti-aircraft fire.

The US casualty figures might have been even worse but for the work of the Allied code breakers throughout the 'Kikusui' campaign. Their warnings of the second phase of the attack on 11 April were widely disseminated, under the cover story that the warning had come from a talkative captured Japanese pilot, and Vice Admiral Marc A. Mitscher, commanding the 1^st Fast Carrier Task Force, ordered all of his carriers' attack aircraft to be disarmed, emptied of fuel and stowed away while the fighters were concentrated for local defence. Meanwhile Admiral Raymod A. Spruance, commander of the 5^th Fleet, was so concerned by the terrible vulnerability of his radar picket destroyers, operating well away from the main strength of the fleet to provide early warning of incoming Japanese attacks, requested the delivery of replacement aircraft and pilots as a matter of the greatest urgency.

Given the number of US ships and the power of their defences (both fighters and anti-aircraft guns) against air attack, only mass attacks by kamikaze aircraft gave the Japanese the chance to swamp the defences, as shown by the first of these on 6 April in 'Kikusui-1' of 6/11 April. On this first day 355 kamikaze machines attacked and sank two destroyers, two ammunition ships and one LST, and damaged some 22 other ships.

This Japanese assault reached an early peak on 6/7 April, when a major assault was launched on the landing fleet around Okinawa, and on the radar picket destroyers stationed farther offshore. There were also weaker attacks on the ships of TG58.1 and TF58.3 to the north-east of Okinawa and those of TF57 to the south of the island. The escort carriers of TF52 east of the island were not targeted.

On 6 April bases on Kyushu saw the launch of 198 kamikaze aircraft, of which 41 returned, 55 were shot down by the fighter cover and 35 by the AA defences. Even so, the attack struck 27 ships, some of them more than once. The picket destroyers Bush and Colhoun, the destroyer minesweeper Emmons, LST-347 and the 7,607-ton ammunition transports Hobbs Victory and Logan Victory were sunk (the former was carrying 7,000 tons of ammunition and exploded off the Kerama-retto, and the latter had to be abandoned and exploded on the following day), the destroyers Leutze, Newcomb and Morris, and the destroyer escort Witter were damaged beyond repair, and the minesweepers Rodman and Defense and the destroyer Mullany suffered damage so severe that they were out of action for the rest of the war.

More moderate damage was inflicted on the destroyers Howorth, Hyman and Haynsworth of TF58, and the destroyer Rook, destroyer escorts Fieberling and Foreman, high-speed minesweeper Emmons, minesweepers Facility, Devastator, Recruit and Ransom, YMS-311 and YMS-321 and LST-447 were also damaged. The British fleet carrier Illustrious of TF57 and the US light carrier San Jacinto of TF58, and the destroyers Bennett, Hutchins and Harrison of TF58 were slightly damaged. In addition, 'friendly fire' damaged the battleship North Carolina, light cruiser Pasadena and destroyer Hutchins. Several tank landing ships were also damaged on the same day by grounding.

On 7 April some 54 kamikaze aircraft of Ugaki’s 5^th Air Fleet took off from bases on Kyushu, and, in addition, some 125 kamikaze aircraft of the army were used on 6/7 April. Of the naval kamikaze aircraft, 24 returned and the others were shot down by the US fighter cover and anti-aircraft defences. The battleship Maryland and picket destroyer Bennett sustained major damage, the fleet carrier Hancock and destroyer escort Wesson sustained moderate damage, and the destroyer Longshaw and minesweeper YMS-81 received minor damage.

There were only individual attacks on 8 and 9 April, when the picket destroyers Gregory and Sterett, the high-speed destroyer transport Hopping and the minesweeper YMS-92 were damaged.

On 8/9 April explosive-filled motor boats attempted attacks from Okinawa, damaging the destroyer Charles J. Badger and the transport Starr.

As a result of these kamikaze attacks, the US Navy lost 466 men killed and 579 injured in the 6/10 April period. Attacks were launched on most days which the weather permitted, and the primary targets were the US carriers and the shipping packed densely off the beaches of Okinawa, which received no fewer than 10 major attacks.

On 11 April 64 kamikaze aircraft, of which 34 returned, were launched against the ships of TF58. The fleet carrier Enterprise, battleship Missouri, destroyers Kidd and Bullard and, off Okinawa, destroyer escort Samuel S. Miles were all hit.

The second stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-1' was 'Kikusui-2' of 12/15 April. On 12 April some 83 navy and 60 army kamikaze aircraft, together with nine Okha manned missiles, were despatched with strong fighter cover to attack the US landing fleet. Of the picket destroyers, Mannert L. Abele was sunk and Stanly damaged by Ohka attack aircraft, while the picket boat LCS(L)-33 was sunk and LCS(L)-57 damaged by kamikaze aircraft. The fleet carrier Essex and destroyer Hale were also damaged by bombs. Other damage casualties were the picket destroyers Purdy and Cassin Young, the destroyer minesweeper Jeffers and, in the area between Okinawa and the Kerama-retto, the battleships Tennessee and Idaho, destroyer Zellars, minesweeper Lindsey and LSM-189 (the last three were out of action until the end of the war), destroyer escorts Rail, Whitehurst, Riddle and Walter C. Wann, and minesweeper Gladiator. The light cruiser Oakland, destroyers Norman Scott and Brush, and destroyer escorts Conklin and Damon M. Cummings were damaged by air attack, and the battleship New Mexico and destroyer Bennion were damaged by 'friendly fire'.

On 14 April 35 of 76 kamikaze aircraft and seven Ohka aircraft attacked and succeeded in damaging the battleship New York, destroyers Dashiell, Hunt and Sightsee (the last being out of action until the end of the war), destroyer escort Connolly, and an oiler.

The final raid of 'Kikusui-2' on 15 April was a comparatively small-scale undertaking involving just 10 kamikaze aircraft, of which eight returned: even so, the two aircraft which got through slightly damaged the destroyer Wilson and oiler Taluga. There were also attacks by suicide motor boats, which damaged the minesweeper YMS-331.

Despite their receipt of signals intelligence, the US Navy’s intelligence branch believed that the Japanese had exhausted their capability with 'Kikusui-2'. Moreover, by 8 April some 82 Vought F4U Corsair fighters of the US Marine Corps' MAG-31 and MAG-33 groups were based on the captured Yontan airfield along with seven night-fighters, and more aircraft were on their way to Okinawa: some 3,521 fighter sorties had therefore been flown from the captured fields by 1 May. Officers who had been through kamikaze attacks in the Philippine islands observed that the individual effectiveness of the kamikaze aircraft was not as great as those used in the earlier campaign, and this estimation was confirmed by the attack statistics. However, the captains of some destroyers had come to the conclusion that nothing short of a 5-in (127-mm) shell could reliably stop a kamikaze aeroplane, and that a single destroyer on radar picket duty without twilight fighter cover was little more than a sitting duck. The night-fighters did not have their radar installed and calibrated until 14 April. Moreover, while the kamikaze aircraft had lost some of their individual capability since the Philippine islands campaign, they were now considerably more numerous.

The third stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-2' was 'Kikusui-3' of 16/17 April. Ugaki’s 5^th Air Fleet resumed operations on 16 April with the launch of 126 kamikaze aircraft, of which 42 returned, as six Ohka manned missiles. On 17 April some 49 aircraft, of which 30 returned, were used. In attacks on TF58, the fleet carrier Intrepid was badly damaged and on 17 April the battleship Missouri and destroyer Benham were less severely damaged. (After the departure of Intrepid for repair, TG58.2 was disbanded and its ships distributed among TG58.1, TG58.3 and TG58.4.)

The kamikaze attacks were now concentrated on the landing fleet, particularly the picket destroyers. Laffey was attacked by 22 aircraft: seven were shot down by fighters and nine by the anti-aircraft defences, but the destroyer was hit by six kamikaze aircraft and four bombs, resulting in 31 men killed and 72 wounded, but the ship was nonetheless brought into harbour. The destroyer Pringle was sunk, the destroyer Bryant and minelayer Harding were damaged beyond repair, and the minesweeper Hobson was so badly damaged that she was out of action for the rest of the war. The destroyer Wilson, destroyer escort Bowers, oiler Taluga, and picket boats LCS(L)-116 and LCS-51 sustained lesser damage.

Throughout 'Kikusui', the US Navy found it very difficult to find and implement any adequate response to the kamikaze attackers. After 10 April, the more exposed radar picket stations were assigned two destroyers and four adapted LCS support landing ships. However, by the time the 5^th Fleet had undergone the 'Kikusui-5' attack, there were clear signs of deteriorating morale, particularly among the crews of the picket destroyers. By May 16, radar stations were operating on Ie-shima island and Hedo-saki headland, and the number of picket stations could be reduced to five. The carriers of TF58 also launched attacks on Kyushu on 15/16 April 1945, achieved surprise and claimed to have shot down 29 aircraft and destroyed 51 aircraft on the ground, which probably reduced the strength of 'Kikusui-3' to a marked degree. However, by this time the Japanese had become highly adept at dispersing their aircraft over the many small airfields available on the home islands.

The fourth stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-3' was 'Kikusui-4' of 27/30 April, in which Ugaki’s 5^th Air Fleet made its main effort on 28 April, when some 65 navy and 60 army kamikaze aircraft being despatched from Kyushu. The destroyer Hutchins and the high-speed destroyer transport Rathburne were damaged beyond repair. The destroyer Ralph Talbot and the destroyer escort England were damaged on 27 April, the destroyers Wadsworth, Daly, Twiggs and Bennion, minesweeper Butler, hospital ship Comfort and casualty transport Pinkney were damaged on 28 April, the destroyers Hazelwood and Haggard and the minelayers Shannon and Harry F. Bauer on 29 April, and the minelayer Terror and destroyer Bennion once again on 30 April. Haggard and Pinkney were out of action for the rest of the war.

The fifth stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-4' was 'Kikusui-5' of 3/9 May. Attacks by 75 navy and 50 army kamikaze aircraft sank the destroyers Little, Luce and Morrison on picket duty and also LSM(R)-190, LSM(R)-195 and LSM(R)-194. The destroyer Aaron Ward was damaged beyond repair, while the destroyer Ingraham and minelayer Shea (hit by an Okha manned missile) were put out of action until the end of the war.

Less severe damage was sustained by the destroyers and destroyer minesweepers Macomb, Bache, Lowry, Massey, Gwin and Cornell, and also by LCS(L)-25.

Operating with the support group off Okinawa, the light cruiser Birmingham was damaged on 3 May, the minesweepers Gayety, Hopkins, YMS-327 and YMS-331 on 4 May, and the tenders St George and Pathfinder on 5 May. On 9 May the destroyer escorts Oberrender and England were damaged beyond repair. In all, there were 605 US dead and 806 injured.

The sixth stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-5' was 'Kikusui-6' of 10/20 May. On 10 May new mass attacks began with sorties by 70 navy and 80 army kamikaze aircraft. On the picket stations from 10 to 13 May, the destroyers Evans and Hugh W. Hadley and LCS(L)-88 were damaged beyond repair, and the destroyer Bache and the destroyer escort Bright were put out of action until the end of the war. The fleet carrier Bunker Hill was badly damaged by the impacts of two kamikaze aircraft.

Off Okinawa, the battleship New Mexico was hit heavily on 12 May but remained in action until 28 May.

On 17 May the destroyer Douglas H. Fox was put out of action until the end of the war by a kamikaze hit.

On 18 May the destroyer Longshaw was stranded off Okinawa and severely damaged by Japanese gunfire from the shore and the high-speed destroyer transport Sims was damaged.

On 20 May LST-808 was sunk, and the destroyer Thatcher and high-speed destroyer transport Chase were damaged beyond repair, and the destroyer escort John C. Butler was slightly damaged. In all, there were 227 US dead and 370 injured.

The seventh stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-6' was 'Kikusui-7' of 24/26 May, which saw a limited change in the Japanese attacks including the 'Gi' (iii) kamikaze air-landing assault on Yontan airfield during the night of 27/27 April, and a concentration on the bombardment and transport vessels while the radar pickets were largely ignored. The new wave of attacks was started by 65 navy and 100 army kamikaze aircraft. On picket duty the destroyer Stormes was severely damaged, and LCS(L)-121 was slightly damaged. Most of the attacking aircraft flew round the end of the radar picket line and attack the ships off Okinawa, in the course of which the high-speed destroyer transport Bates and LSM-135 were sunk, the high-speed destroyer transports Roper and Barry and the minesweepers Butler and Spectacle were damaged beyond repair, the destroyer escort O’Neill was severely damaged, and the destroyer escort William C. Cole, the high-speed destroyer transport Sims and a Liberty ship were slightly damaged.

The severely damaged Barry was later towed out as a decoy for later kamikaze attacks, and was sunk on 21 June, along with her towing vessel.

On 26 May attacks by individual kamikaze aircraft damaged the destroyer minesweeper Forrest, submarine chaser PC-1603 and tender Dutton.

The eighth stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-7' was 'Kikusui-8' of 27/29 May. Some 60 navy and 50 army kamikaze aircraft were committed. On the radar picket stations, the destroyer Drexler was sunk, Braine severely damaged and Anthony slightly damaged. Also slightly damaged were LCS(L)-52 and LCS(L)-119. Off Okinawa, the minesweeper Southard, the troop-carrying destroyer transports Loy and Rednour, and the transport Sandoval took kamikaze impacts. On 29 May the destroyer Shubrick and high-speed destroyer transport Tatum were damaged, the former beyond repair.

The crews of repair ships were able to restore a large number of the damaged vessels in the roads off the Kerama-retto.

The ninth stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in immediate succession to 'Kikusui-8' was 'Kikusui-9' of 3/7 June. Some 20 Japanese navy and 30 army kamikaze aircraft implemented the operation off Okinawa. On 3 June the freighter Alleghani was damaged. On 5 June the battleship Mississippi and heavy cruiser Louisville were damaged. On 6 June the light minelayers Harry F. Bauer and J. William Ditter and on 7 June the escort carrier Natoma Bay, destroyer Anthony and picket boat LCI(L)-90 received hits, the last last two being damaged beyond repair. On 10 June a single kamikaze aeroplane hit and sank the destroyer William D. Porter.

The tenth and final stage of the kamikaze air campaign against the US naval forces off Okinawa during 'Iceberg' in succession to 'Kikusui-9' was 'Kikusui-10' of 21/22 June. Some 30 Japanese navy and 15 army kamikaze aircraft implemented the operation off Okinawa and the Kerama-retto. The attacks damaged the destroyer escort Halloran, seaplane tenders Curtiss and Kenneth Whiting, minesweeper Ellyson, LST-534 and the picket boats LSM-59 and LSM-213.

The damage to the US Navy during the Okinawa campaign was 26 ships sunk and another 164 damaged, plus 4,900 personnel killed and 4,800 wounded, mostly by the kamikaze aircraft. The kamikaze aircraft campaign ended on 22 June, by which time some 1,900 sorties had been launched and 1,465 aircraft expended, most of them shot down by the fighters or immensely thick barrages of heavy and medium anti-aircraft fire.