'Inmate' was a British, Canadian and New Zealand naval bombardment of Japanese installations on Truk atoll in the Caroline islands group (12/16 June 1945).

These attacks on isolated islands during 14 and 15 June 1945 were designed to provide combat experience for the fleet carrier Implacable and several of the British Pacific Fleet’s cruisers and destroyers ahead of their involvement in more demanding operations off the Japanese home islands.

On 14 June British aircraft conducted a series of raids against Japanese positions at Truk island, and on the morning of the following day several islands were bombarded by British and Canadian cruisers, though only one of the four warships involved achieved any success. More air attacks were delivered during the afternoon and night of 15 June before the Allied force returned to its base.

The attack on Truk was considered successful for the Allied force, with the ships and air units gaining useful experience while suffering two fatalities and the loss of seven aircraft to combat and accidents. The damage to the Japanese facilities in the atoll, which had been repeatedly attacked during 1944 and 1945, was modest.

The British Pacific Fleet had been established under the command of Admiral Sir Bruce Fraser in November 1944 as the UK’s chief contribution to Allied operations against Japanese positions in the Pacific. The fleet’s base had been established in Sydney of the east coast of Australia, and most of its ships arrived there in February 1945. From a time late in March to late in May 1945, aircraft flying from the British Pacific Fleet’s four fleet carriers frequently attacked Japanese airfields on islands to the south of Okinawa to support the US forces which were attempting to capture the island in 'Iceberg'. These operations concluded on 24 May, when the British Pacific Fleet began the long journey back to Sydney for a period of rest and maintenance.

The fleet carrier Implacable was despatched from the United Kingdom in February 1945 to reinforce the British Pacific Fleet, and reached Sydney on 8 May. On 24 May Implacable departed Sydney, and reached the British Pacific Fleet’s forward base at Manus island, in the Admiralty islands group to the north of New Guinea, five days later. The main body of the British Pacific Fleet arrived at Manus to refuel on 30 May, and most of its ships continued to Sydney on 1 June. Implacable remained at Manus, which she and her air group used as a base for intensive training. As part of the preparations for the British Pacific Fleet’s return to combat, the commander of the fleet’s combat force, Vice Admiral Sir Bernard Rawlings, decided at this time to despatch Implacable and several other recently arrived warships to attack the Japanese positions at Truk. The purpose of this operation was to ensure that the warships' crews had recent combat experience before the British Pacific Fleet embarked on operations off Japan during July. Rawlings’s initial orders for the attack specified that it was to involve two days of air attacks on Japanese airfields, and the crews of the ships involved, including Implacable's aircrews, were not informed that the primary purpose of the operation was training.

During the early years of the Pacific War of World War II, Truk atoll in the Caroline islands group had been an important base for the Imperial Japanese navy, which made extensive use of the facilities constructed there before the outbreak of hostilities. However, Truk had been isolated by the rapid Allied advances in the Pacific during 1943 and early in 1944, and had thus ceased to be a significant base after being heavily attacked by the US Fast Carrier Task Force during 'Hailstone' in February 1944. Even so, there remained the possibility that the facilities at Truk could have been used to raid the important Allied facilities which had been established in the Mariana islands group or the major US Navy anchorage at Ulithi atoll in the Caroline islands group. To deny the Japanese any such possibility, they had been repeatedly attacked by US Navy aircraft carriers which were preparing to join the Fast Carrier Task Force and by US Army Air Forces' heavy bomber units: like the British operation in June 1945, these raids were used to provide combat experience for US air crews. The Japanese forces at Truk conscripted local civilians for the rapid repair of the damage caused to airfields by these raids, and the garrison’s anti-aircraft units also fired upon all of the raids, though the scale of this resistance decreased over time.

In the middle of 1945, the Japanese garrison at Truk remained large in numerical terms, but had no offensive capacity. As of May that year, the garrison comprised some 13,600 men of the Imperial Japanese army under the command of Lieutenant General Shunzaburo Mugikura and 10,600 men of the Imperial Japanese navy under the command of Vice Admiral Chuichi Hara. A large number of coastal artillery and anti-aircraft batteries protected the islands, but no warships and only a small number of aircraft were stationed there. Radar stations on the islands provided warning of most incoming raids. The Japanese forces regarded Truk’s air defences as inadequate even before the start of the Allied bombardment of the atoll.

The garrison of Truk received few shipments of reinforcements or supplies following the capture of the Palau islands group by US forces in September 1944. The garrison’s main activity from the middle of 1944 was growing food to sustain itself. The tropical conditions and damage caused by air attacks complicated this effort, and most of the Japanese personnel were malnourished. Even so, the garrison also took extensive measures to protect the atoll from amphibious assault, and stored large quantities of food and other vital supplies against such an eventuality. Following the end of the war in August 1945, US forces found that the garrison still possessed sufficient ammunition to supply its gun batteries for at least 30 days of combat.

The British Pacific Fleet’s force for 'Inmate' was designated Task Group 111.2, and comprised the 4^th Cruiser Squadron and 24^th Destroyer Flotilla. The ships assigned to the 4^th Cruiser Squadron were Implacable, the escort carrier Ruler, the light cruisers Swiftsure, Newfoundland, Canadian Uganda and New Zealand Achilles. The 24^th Destroyer Flotilla comprised Troubridge, Teazer, Tenacious, Termagant and Terpsichore. TG111.2 was commanded from Implacable by Rear Admiral E. J. P. Brind. While Implacable, Newfoundland and the destroyers had only recently arrived in the Pacific, all of TG111.2’s other ships had seen combat off Okinawa. Implacable's most recent combat experience was a series of air attacks against the German forces and installations in Norway late in 1944.

Implacable embarked 80 aircraft, which was the largest number to be operated by any of the British Pacific Fleet’s aircraft carriers. The air group included No. 38 Naval Air Wing, whose Nos 801 and 880 Squadrons were equipped with 48 Supermarine Seafire single-seat fighters. The other units assigned to the carrier were No. 828 Squadron with 21 Grumman TBF Avenger torpedo bombers and No. 1771 Squadron with 11 Fairey Firefly two-seat fighters. Ruler's task was to provide a 'spare deck' for Implacable's air group, and the escort carrier embarked only a single Supermarine Walrus search and rescue aeroplane of No. 1701 Squadron.

TG111.2 departed Manus island on 12 June. While en route to Truk, its orders were broadened to include a cruiser bombardment of Japanese positions on Truk. This change was made as the cruisers were expected to be used against shore targets during future operations. In preparation for these bombardments, the ships of the task group conducted gunnery exercises during their passage to the north. Ahead of the attacks on Truk, a US Navy submarine took up position near the atoll to rescue any British airmen who crashed into the sea.

The Allied warships reached the flying-off position for Implacable's air group at 05.30 on 14 June, and 10 minutes some 12 Seafire and two Firefly aircraft were launched. The Seafire fighters strafed a radar station and an airfield on Moen island, and the Fireflies flew a reconnaissance of the atoll. A Seafire equipped with a reconnaissance camera also photographed Japanese installations, and the resulting photographs were used to plan further air attacks and bombardments. One of the Seafire fighters was shot down and its pilot killed while attacking the airfield, the only British aircraft to be lost in combat during 'Inmate'.

Implacable launched attacks every 135 minutes for the rest of 14 June. These attacks generally comprised five Avenger aircraft armed with bombs and four Firefly aircraft armed with cannon and rockets. The day’s last attack was made by 12 Seafire aircraft, which dive-bombed fuel tanks on Moen island. Several of the tanks were cracked open, but the absence of fires indicated that they were empty. The British aircraft reported finding few worthwhile targets, but they were engaged by the Japanese anti-aircraft defences throughout the day. All of the attacks were escorted by Seafire fighters, but no Japanese aircraft were encountered in the air. During the night of 14/15 June two Avenger machines operated over the atoll in an attempt to prevent the Japanese from repairing the airfield on Moen: the aircraft were taken under fire and tracked by searchlights, but suffered no casualties.

Patrols of eight Seafire fighters from No. 38 Naval Air Wing patrolled over TG111.2 for much of 14 June without encountering Japanese aircraft. Ruler was employed as the 'base' for this task, and refuelled and rearmed Seafire fighters between sorties. The use of the escort carrier as a 'spare deck' was considered successful, especially as a group of six Seafire fighters short of fuel was able to land on Ruler when Implacable was caught in a squall and could not undertake flight operations. During the morning of 14 June Ruler's Walrus was blown overboard by a tropical squall and destroyed. Aerial search and rescue support for the force was provided by US Navy Consolidated PBY Catalina flying boats which flew in relay near Truk, but these aircraft were not required as destroyers were able to rescue the crews of ditched aircraft.

The surface bombardment element of 'Inmate' took place during the late morning of 15 June. The bombardment force was organised into three task units comprising both cruisers and destroyers: Achilles and Uganda (with Brind embarked) operated with Tenacious, Newfoundland with Troubridge, and Swiftsure with Teazer. This left the protection of the carriers to just two destroyers. Each task unit was also assigned two Seafire fighters to spot their gunfire. The destroyers assigned to the bombardment task units were responsible for counter-battery fire on any Japanese guns which fired on the cruisers, and for generating smokescreens if necessary. Throughout the bombardments the carriers steamed some 10 miles (16 km) to the east of Truk, and maintained a combat air patrol over the area.

The cruisers experienced differing levels of success. Newfoundland initially attacked coastal gun batteries, but these latter did not respond. She also successfully bombarded the airfield on Eten island. The attacks of Achilles and Uganda on a seaplane base on Dublon island caused only insignificant damage and were marred by communications problems between the ships and their Seafire spotters. As Achilles steamed away from Truk, her anti-aircraft gunners fired on two aircraft approaching from the direction of the atoll, until they were identified as British Avenger machines.

Swiftsure's bombardment of Moen island was particularly unsuccessful. The initial rounds fired by her guns landed well away from their targets, and attempts to correct her gunfire led to a further deterioration in accuracy. Her gunnery officer judged that the ship’s fire-control equipment was defective, and ordered the 6-in (152-mm) main gun turrets to fire under local control. This also proved unsuccessful as the gunners were unable to sight targets on the shore. After sailing closer to Moen island, the ship attempted to engage Japanese positions with several of her 4-in (102-mm) secondary guns. However, the ammunition for these weapons was fitted with proximity fuses intended for use against aircraft, and exploded in the palm trees above their targets. As the fallen foliage hid the Japanese positions, further attacks were ineffective. A subsequent investigation found that a faulty split pin had fallen out of Swiftsure's Admiralty Fire-Control Table, most likely as a result of concussion from the initial shots, causing it to provide highly inaccurate results to the guns. After the end of the bombardment at 11.10, the ships involved rejoined the carriers.

Further air attacks were made during 15 June. In the afternoon, two groups of Avenger aircraft attacked a floating dry dock and several oil tanks. During the night which followed, six Avenger aircraft armed with bombs supported by two flare-dropping Avenger machines flew the final attack of 'Inmate', but it is believed that most of their bombs fell into the sea.

After the end of the night attack, TG111.2 departed for Manus island. On 16 June a Japanese aeroplane was detected on radar, and one Seafire was detached from the combat air patrol to intercept, but the fighter’s pilot had to abandon the attempt as a result of a mechanical problem. The task group reached Manus island on 17 June, and continued training exercises there until the rest of the British Pacific Fleet arrived on 4 July en route to further operations off Japan. All the warships at Manus island departed on 6 July to join the Fast Carrier Task Force in attacks on the Japanese home islands. Implacable and the other ships of the British Pacific Fleet operated against Japan from 17 July to 12 August, during which time the fleet flew air attacks and participated in several bombardments of Japanese coastal cities and towns. On 12 August most of the British Pacific Fleet’s ships, including Implacable, departed for a period of maintenance and rest at Sydney.

A new TG111.2 was created by the British Pacific Fleet at Sydney on 12 August. This comprised the veteran fleet carrier Indomitable, three newly arrived light fleet carriers, two battleships, two or three cruisers and nine destroyers. It was planned that these ships would reinforce the British Pacific Fleet for the planned 'Olympic' invasion of Japan, but lacked recent combat experience. Consideration was given to using the force to attack Truk once again in an operation possibly also including a landing on the atoll by Australian or New Zealand land forces, but this was rendered unnecessary by Japan’s surrender on 15 August.

US air units attacked Truk regularly until the end of the war, and the atoll’s garrison formally surrendered at a ceremony conducted on the board the US heavy cruiser Portland on 2 September, the day on which Japan’s general surrender documents were signed. The Japanese soldiers and sailors were repatriated from Truk during November and December 1945.

In 'Inmate', TG111.2’s aircraft flew 103 offensive sorties during daylight and a further 10 at night. A total of 103 defensive sorties were also undertaken. In addition to the Seafire shot down on 14 June and the loss of Ruler's Walrus, five Avenger aircraft were destroyed in take-off accidents: one of these aircraft crashed into the sea as a result of an error in attaching it to Implacable's catapult, and resulted in the death of its pilot. The other four Avenger aircraft ditched as a result of engine malfunctions, with no fatalities. Two Seafire fighters, both flown by the same man, were also damaged in landing accidents.

The Japanese losses were modest. The British assessed that two Japanese aircraft had been destroyed and another three damaged during attacks on airfields at Truk. Damage was also believed to have been inflicted on the airfields, floating dry dock, oil tanks, other harbour installations and ships. Following the operation, Brind judged that rockets had proved themselves more useful than bombs, and was critical of the gunnery of all the cruisers other than Newfoundland. Members of the Japanese garrison told US Strategic Bombing Survey investigators after the war that the British raid had resulted in almost no damage. The most significant loss was the destruction of part of the garrison’s records, which led to a decision to bury the remaining records.