Operation Inmate

Background

The British aircraft carrier HMS Implacable was dispatched from the United Kingdom in February 1945 to reinforce the British Pacific Fleet (BPF). The ship arrived at the BPF's main base at Sydney in Australia on 8 May. At this time, the main body of the BPF was operating off Okinawa in the North Pacific. On 24 May Implacable departed Sydney, and arrived at the BPF's forward base at Manus Island on the 29th of the month. Several days later the remainder of the BPF arrived at Manus to refuel before most of its ships continued to Sydney for a period of rest and maintenance.

As part of the preparations for the BPF's return to combat, Admiral Bernard Rawlings – the commander of the fleet's combat force – decided to dispatch 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 BPF commenced operations off Japan during July.

During the early years of the Pacific War, Truk Atoll in the Caroline Islands had been an important base for the Imperial Japanese Navy (IJN), using facilities which had been constructed there before the outbreak of hostilities. However, it was isolated by the rapid Allied advances in the Pacific during 1943 and early 1944, and ceased to be a significant base after being heavily attacked by the United States Navy's Fast Carrier Task Force during Operation Hailstone in February 1944. Nevertheless, the facilities at Truk could have potentially been used to raid the important Allied facilities which had been established in the Mariana Islands or the major US Navy anchorage at Ulithi. To prevent the islands from being used for this purpose, they were repeatedly attacked by US Navy aircraft carriers which were preparing to join the Fast Carrier Task Force and United States Army Air Forces heavy bomber units which had recently arrived in the region; like the British operation in June 1945, these raids were also conducted to provide combat experience for the American airmen.

By mid-1945 the Japanese garrison at Truk remained large, but had no offensive capacity. As of May that year, the atoll's garrison comprised around 13,600 Imperial Japanese Army personnel commanded by Lieutenant General Shunsaburo Mugikura and 10,600 IJN personnel under Vice Admiral Chuichi Hara. Several coastal artillery batteries and a number of small-calibre anti-aircraft guns protected the islands, but no warships and only a small number of aircraft were stationed there at the time of Operation Inmate. The garrison received few reinforcements following the capture of the Palau islands by US forces in September 1944, and historian David Hobbs has stated that it had been "reduced to starving impotence" by the time of Operation Inmate.

The BPF's Truk attack force was designated Task Group 111.2, and comprised the 4th Cruiser Squadron and 24th Destroyer Flotilla. The ships assigned to the 4th Cruiser Squadron were Implacable, the escort carrier HMS Ruler and cruisers HMS Swiftsure, Newfoundland, HMCS Uganda and HMNZS Achilles. The 24th Destroyer Flotilla was made up of Troubridge, Teazer, Tenacious, Termagant and Terpsichore. The Task Group was commanded from Implacable by Rear Admiral E.J.P. Brind. While Implacable, Newfoundland and the destroyers had recently arrived in the Pacific, all the other ships assigned to Task Group 111.2 had seen combat off Okinawa. Implacable's most recent combat experience was a series of air strikes conducted against German forces in Norway during late 1944.

Implacable embarked 80 aircraft, which was the largest to be operated by any of the BPF's aircraft carriers. The air group included 38 Naval Air Wing, whose 801 and 880 Naval Air Squadrons operated 48 Supermarine Seafire fighter aircraft. The other units assigned to the carrier were 828 Naval Air Squadron with 21 Grumman TBF Avenger torpedo bombers and 1771 Naval Air Squadron, which was equipped with 11 Fairey Firefly fighters. Ruler was intended to be used as a "spare deck" for Implacable's air group, and embarked only a single Supermarine Walrus search and rescue aircraft from 1701 Naval Air Squadron.

14 June

Task Group 111.2 departed from Manus Island on 12 June. While en route to Truk, its orders were broadened from attacking the atoll with air strikes for two days to also include a cruiser bombardment. This change was made as the cruisers were expected to be used against shore targets during future operations. In preparation for these bombardments, the Task Group conducted gunnery exercises during its voyage 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 5:30 am on 14 June. Ten minutes later, twelve Seafires and two Fireflies were launched. The Seafires strafed a radar station and an airfield on Moen island, and the Fireflies reconnoitred the atoll. A Seafire equipped with a reconnaissance camera also photographed Japanese installations; these photos were used to plan further air attacks and bombardments. One of the Seafires was shot down while attacking the airfield, resulting in the death of its pilot. This was the only British aircraft to be lost in combat during Operation Inmate.

Implacable launched strikes every two and a quarter hours for the remainder of 14 June. These generally comprised five Avengers armed with bombs and four Fireflies with rockets and cannon. The final attack of the day was made by twelve Seafires which dive bombed fuel tanks on Moen island. While several of the tanks were cracked open, it appeared that they were empty. This attack was the first time that Seafires had been used as fighter bombers in the Pacific. The British aircraft were fired on by Japanese anti-aircraft guns throughout the day, and reported finding few worthwhile targets. All of the strikes were escorted by Seafires, but no Japanese aircraft were encountered in the air. During the night of 14/15 June two Avengers operated over the atoll in an attempt to prevent the Japanese from repairing the airfield on Moen; these aircraft were also fired on and tracked by searchlights but did not suffer any casualties.

38 Naval Air Wing maintained a protective combat air patrol of eight Seafires over Task Group 111.2 throughout 14 June, but these did not encounter any Japanese aircraft. Ruler was used as the base for this task, and refuelled and rearmed Seafires between sorties. The use of the escort carrier as a "spare deck" was considered successful, especially as a group of six Seafires which may have run out of fuel were able to land on Ruler when Implacable was caught in a squall and unable to receive them. 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 subsequently provided by US Navy Consolidated PBY Catalina flying boats which flew in relay near Truk. However, these aircraft were not required, with the crews of aircraft which were forced to ditch being rescued by destroyers.

15 June

The surface bombardment 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 was accompanied by Troubridge and Swiftsure by Teazer. Each task unit was assigned two Seafires to spot their gunfire. This left the aircraft carriers with only two destroyers for protection. Throughout the bombardments the carriers sailed 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 did not fire on her or her escorting destroyer. She subsequently successfully bombarded the airfield on Eten Island. The attacks by Achilles and Uganda on a seaplane base on Dublon Island did not cause any damage and were marred by communications problems between the ships and their spotting Seafires. As Achilles sailed away from Truk, the cruiser's anti-aircraft gunners fired on two aircraft which approached her from the direction of the atoll until they were identified as British Avengers.

Swiftsure's bombardment of Moen 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-inch (15 cm) gun turrets to fire under local control. This also proved unsuccessful as the gunners were unable to sight targets on the shore. Swiftsure subsequently sailed closer to the shore, and attempted to engage Japanese positions with several of her 4-inch (10 cm) guns. However, the ammunition for these weapons was fitted with proximity fuses intended for use against aircraft, and exploded in the palm trees above her targets. As the fallen foliage camouflaged 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 due to concussion from the initial shots, leading it to provide greatly inaccurate results to the guns. The bombardment ended at 11:10 am, and the ships involved subsequently rejoined the carriers.

Further air attacks were also conducted on 15 June. During the afternoon, two groups of Avengers attacked a floating dry dock and several oil tanks. That night six Avengers armed with bombs supported by two flare-dropping Avengers conducted the final British attack on Truk, but it is believed that most of their bombs landed in the sea. This was the BPF's first large-scale night operation.

At the conclusion of the night strike Task Group 111.2 departed for Manus Island. On 16 June a Japanese aircraft was detected by radar. While one of the Seafires was detached from the combat air patrol to intercept it, the fighter's pilot had to abandon the attempt due to a mechanical problem. The Task Group arrived at Manus Island on 17 June, and continued training exercises there until the remainder of the BPF arrived on 4 July en route to further operations off Japan. All of the warships at Manus sailed on 6 July to join the Fast Carrier Task Force in attacks on the Japanese home islands.

Aftermath

During Operation Inmate, Task Group 111.2's aircraft flew 103 offensive sorties during daylight and a further 10 at night. A total of 103 defensive sorties were also conducted. In addition to the Seafire shot down on 14 June and Ruler's Walrus, five Avengers were destroyed due to accidents while taking off; one of these aircraft crashed into the sea due to an error in attaching it to Implacable's catapult, resulting in the death of its pilot. The other four Avengers ditched due to engine malfunctions but their crews did not suffer any fatalities. Two Seafires, both piloted by the same airman, were also damaged in landing accidents. A book published to mark the 50th anniversary of the BPF described these losses as low by the standards of 1945.

Japanese losses were also believed to be 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 that were attacked. Following the operation, Brind assessed that rockets had proven more useful than bombs, and was critical of the gunnery of all the cruisers other than Newfoundland.

The historian David Hobbs has judged that Operation Inmate "provided realistic and useful training for ships that were newly arrived in the Pacific and everyone, including Swiftsure's embarrassed gunners, ... learned something". Peter C. Smith has also noted that while few targets were located, the raids provided useful experience for Implacable's air crew and "the standards of flight launch and recovery attained during the operation were to stand them in good stead in the months ahead". Similarly, British official historian Stephen Roskill concluded that Operation Inmate achieved its goals.

A new Task Group 111.2 was formed by the BPF at Sydney on 12 August 1945. This force comprised the veteran aircraft carrier HMS Indomitable, three newly arrived light fleet carriers, two battleships, two or three cruisers and nine destroyers. These ships were intended to reinforce the BPF for the planned invasion of Japan, but lacked recent combat experience. Consideration was given to using the force to attack Truk again, with this operation possibly also including an invasion of the atoll by Australian or New Zealand forces, but this came to nothing as the war ended with Japan's decision to surrender on 15 August.