'C' (iii) was a Japanese major naval raid into the Indian Ocean and Bay of Bengal by Vice Admiral Chuichi Nagumo’s 1^st Air Fleet from an advanced base at Staring Bay in Celebes island, part of the Netherlands East Indies recently seized by the Japanese in 'H' (i) (31 March/9 April 1942).

Although the British feared that the Japanese might attempt to invade Ceylon as a logical successor to their 'B' (iii) seizure of Burma. The Japanese in fact lacked both the troops and the transport vessels which would have been required for an undertaking of this nature, which could effectively have denied the British use of the Indian Ocean, and thus severely limited if not cut this maritime line of communications between Australasia and the Middle East and UK. The Japanese instead planned and executed a raid intended to disrupt British defence plans in the theatre.

The British plans were based on the warships of Vice Admiral Sir James Somerville’s Eastern Fleet, land forces comprising just six infantry brigades, and air forces based on a very modest number of largely obsolescent if not actually obsolete warplanes.

The Japanese navy saw its foray into the Indian Ocean during the first part of April 1942 as an essential component in the establishment of Japan’s planned defensive perimeter against inevitable Allied counter-offensives. Within this overall scheme, the Imperial Japanese navy’s headquarters schemed a raid by Nagumo’s Carrier Strike Force, 1^st Air Fleet, against targets in Ceylon, where the naval bases at Colombo and Trincomalee were the hearts of British naval power in the Indian Ocean. The Imperial Japanese navy expected that surprise attacks on these two bases would inflict major damage on the Royal Navy and thus force the British to withdraw any remnants of their Eastern Fleet from the Indian Ocean as far to the west as the Gulf of Suez, East Africa or South Africa. This would give the Japanese a buffer, in front of the defence perimeter from Burma to Singapore, against the inevitable reconstruction of British naval power in the theatre.

Toward the same end, the 2^nd Southern Expeditionary Fleet, one of the components of Vice Admiral Ibo Takahashi’s South-West Area Fleet when this came into existence just as 'C' (ii) ended, carried out a three-pronged attack to destroy British merchant shipping in the Bay of Bengal. In addition to their practical objective of stopping, at least for a time, all shipborne trade to and from ports on the Indian subcontinent’s eastern coast, the Japanese believed that they could strike an important psychological to the British position in India: at a time when most of the British first-line military strength in the theatre was committed to the last stages of the attempt to save Burma from being overrun by the Japanese, the apparent threat of a Japanese seaborne invasion of India might cause panic in India.

The Admiralty was all too aware of the danger to its Eastern Fleet as Burma’s loss continued, and also appreciated that Nagumo’s carrier force might make another raid along the lines already established with its attacks on Pearl Harbor in the Hawaiian islands group on 7 December 1941 and on Darwin in northern Australia on 19 February 1942. Recognition of the danger provided no effective solution, however, for the Royal Navy was already overburdened by the requirements of its existing fronts, and lacked adequate numbers of ships for any of them. Nevertheless, the Combined Chiefs-of-Staff desired the strengthening of the Eastern Fleet in Ceylon so that it could at least hold this important base area. Without Ceylon, essential convoys linking India with Europe and the Western Desert campaign in North Africa would face constant danger.

The first British step was to appoint Somerville, one of the UK’s most capable officers and formerly commander of the Gibraltar-based Force 'H', to succeed Admiral Sir Geoffrey Layton at the head of the Eastern Fleet. Somerville assumed command on 26 March, and Layton then became the commander-in-chief in Ceylon.

Somerville’s intelligence officers estimated that Japanese raids on Colombo and Trincomalee were very probable. Unknown to the Japanese, however, the British were also building a third, albeit more limited, naval base at Addu atoll, some 700 miles (1125 km) to the south-west of Ceylon, on the southernmost of the islands of the Maldive islands group. Intended primarily as an anchorage and fuelling base, Addu atoll lacked defences against submarine and air attack, but could still be used as a refuge and for training. Oil tanks and storage facilities were built on Gan island, together with an airstrip and a flying boat base.

Somerville had no illusions about the capabilities of the Eastern Fleet’s Force 'B' (otherwise the Slow Division), commanded by Vice Admiral A. U. Willis: this was centred on the light carrier Hermes and the old battleships Resolution, Ramillies, Royal Sovereign and Revenge. The capital ships were slow and short-ranged, and the division’s light cruisers (Caledon, Dragon and Free Dutch Jacob van Heemskerck) and destroyers (Griffin, Arrow, Decoy, Fortune, Scout, Australian Norman and Vampire, and Free Dutch Isaac Sweers) constituted a poorly matched multi-national assortment whose ships had not trained together and were also in acute need of repair and refit. Somerville knew that as they would be of no help against a carrier raid, it would be best to keep these vessels in reserve for other work, especially the escort of convoys plying the Indian Ocean.

The task of repulsing the anticipated raids would thus rest with the Eastern Fleet’s Force 'B' (otherwise the Fast Division), whose ships comprised the fleet carriers Indomitable and Formidable, the battleship Warspite, the heavy cruisers Dorsetshire and Cornwall, the light cruisers Enterprise and Emerald, and the destroyers Paladin, Panther, Hotspur, Foxhound, and Australian Napier and Nestor.

Somerville’s plan of action was perfectly orthodox: he intended to keep his fleet beyond the range of Japanese reconnaissance aircraft during the day, and then to close during the night in order to be within the attack range of his own aircraft at daybreak.

The airfields of Ceylon contained a useful number of aircraft: that outside Colombo, for example, was home to 42 machines in the form of 22 Hawker Hurricane, 14 Supermarine Spitfire and six Fairey Fulmar single-engined fighters, and a local racetrack had been converted into an additional airstrip; and that outside Trincomalee was home to Bristol Blenheim twin-engined light bombers which, it was somewhat optimistically hoped, could deliver effective attacks on the Japanese carriers.

Somerville was told, on the basis of 'Ultra' intelligence, that an attack on Ceylon could be expected as early as 1 April, and his information on the size of Nagumo’s force was quite accurate: the primary striking force comprised the fleet carriers Akagi of Nagumo’s own 1^st Carrier Squadron, Hiryu and Soryu of Rear Admiral Tamon Yamaguchi’s 2^nd Carrier Squadron, and Shokaku and Zuikaku of Rear Admiral Chuichi Hara’s 5^th Carrier Squadron: the 1^st Air Fleet's sixth organic carrier, Kaga, sister ship of Akagi, had returned to Japan on 2 March with engine problems. Other ships available to Nagumo were the battleships Haruna, Kirishima, Hiei and Kongo of Vice Admiral Gunichi Mikawa’s 3^rd Battleship Squadron, the heavy cruisers Tone and Chikuma of Admiral Hiroaki Abe’s 8^th Cruiser Squadron, and the light cruiser Abukuma of Rear Admiral Sentaro Omori’s 1^st Destroyer Flotilla which otherwise comprised the destroyers Tanikaze, Urakaze, Isokaze and Hamakaze of the 17^th Destroyer Division, Arare, Shiranuhi, Kasumi and Kagero of the 18^th Destroyer Division, and Maikaze, Hagikaze and Akigumo.

This force was supported by the submarines I-2, I-3, I-4, I-5, I-6 and I-7, which departed Penang on on 27 March to take up positions to the west of India with a view to intercepting any British warships which might try to retire to the west.

Departing Staring Bay on Celebes island during 26 March, Nagumo’s ships proceeded to the west of Timor island to reach a position to the south of Java, where they refuelled on 1/2 April.

On 1 April the Japanese destroyer Ayanami departed Penang to Port Blair in the Andaman islands group, which it reached on 4 April, with the 10,009-ton tanker/transport Tatekawa Maru carrying supplies and reinforcements for the Japanese garrison of the islands.

On the same day the Vice Admiral Jisaburo Ozawa’s 'Malay' Force (otherwise the 2^nd Southern Expeditionary Fleet), with the heavy cruisers Chokai and Kumano of Rear Admiral Takeo Kurita’s 7^th Cruiser Squadron supplemented by the heavy cruisers Mikuma, Mogami and Suzuya, the light carrier Ryujo of Rear Admiral Kakuji Kakuta’s 4^th Carrier Squadron, and the light cruiser Yura with the destroyers Fubuki, Shirayuki, Hatsuyuki and Murakumo of the 11^th Destroyer Division departed Mergui in southern Burma, some 230 miles (370 km) to the south-east of Rangoon, to carry out a raid in the Bay of Bengal.

A Supply Force of two destroyers was attached to the 2^nd Southern Expeditionary Fleet, and the 2^nd Southern Expeditionary Force was supported by a Strike Force, Main Body, acting as a Cover Force, while the Screening Force of the light cruiser Kashii, minelayer Hatsutaka and nine destroyers was entrusted with the task of watching for British ships in the area to the north of the Andaman islands group and protecting the eventual withdrawal of the Carrier Strike Force.

On 3/4 April the 2^nd Southern Expeditionary Force waited to the south of the Andaman islands group, and in the process exchanged the 11^th Destroyer Division, which proceeded to Port Blair, for the 20^th Destroyer Division comprising Amagiri, Asagiri, Shirakumo and Yugiri.

On 2 April a Japanese convoy with 46 transport vessels departed Singapore to deliver Lieutenant General Renya Mutaguchi’s 18^th Division to Rangoon. The convoy’s escort was provided by the light cruiser Kashii, the destroyers Hatakaze and Shikinami, and the submarine chaser Ch-8. Two days later Kashii and Shikinami were replaced by an escort force from Penang comprising the minelayer Hatsutaka and destroyers Asakaze, Harukaze and Matsukaze of the 5^th Destroyer Division. The convoy reached Rangoon on 7 April without incident.

During the evening of 4 April the 3^rd Destroyer Flotilla, comprising the light cruiser Sendai and the destroyers Fubuki, Hatsuyuki, Murakumo and Shirayuki of the 11^th Destroyer Division and Isonami, Uranami and Ayanami of the 19^th Destroyer Division, departed Port Blair to take up a covering position to the west of the Andaman islands group until 8 April.

Meanwhile, in accord with the tactic on which he had decided, Somerville therefore gathered his Fast Division and attempted for three days and two nights to be in his alternating defence and attack positions in the area to the south of Ceylon. On the evening of 2 April he decided that either the information about the attack’s date was erroneous or that Nagumo was seeking to wait him out and catch the British ships in harbour at night. This was a real possibility, for the British ships' water supplies were low, and they would soon have to return.

Another factor which had to be taken into consideration was the known availability to the Japanese, in the Indian Ocean, of six submarines, whose threat made any concentration of the Eastern Fleet in the same area an invitation to ambush. In fact Nagumo was not trying to outwait Somerville, but was making his planned westerly approach to the south of Ceylon. In fact the only error lay in British intelligence’s perception of the raid materialising several days before in fact it did.

Somerville then made what was to prove a costly error. At 21.00 on 2 April he sent the bulk of his force toward Addu atoll for replenishment, and on the following morning again split his force and sent back to Colombo the cruisers Dorsetshire and Cornwall, the first to resume an interrupted refit and the second to escort a convoy. The carrier Hermes and destroyer Vampire were sent to Trincomalee to resume preparations for the forthcoming 'Ironclad' amphibious landing on Madagascar.

Just as the British ships reached Addu atoll late in the afternoon of 4 April, a British reconnaissance aeroplane (one of the six Consolidated Catalina twin-engined flying boats based in Ceylon) sighted the Japanese carrier force steaming to the north in a position some 415 miles (670 km) to the south of Dondra Head, the southernmost part of Ceylon, and reported the fact by radio before it was shot down by a Japanese carrierborne fighter.

Somerville immediately appreciated that the Japanese raid was now starting, with the first attack inevitably taking place on the following morning, 5 April, while he was 700 miles (1125 km) from Colombo and unable to intervene. The British now scrambled to rectify the situation. Based at Colombo, Layton ordered all the elements of the island’s defence to immediate readiness from 03.00 on 5 April. Most of the ships in the harbour had already been sent to sea on or after 28 March, and now the rest were despatched.

The heavy cruisers Dorsetshire and Cornwall sortied at 22.00 for Addu atoll, and at Trincomalee, the light carrier Hermes and destroyer Vampire were also ordered to Addu atoll as soon as they had completed refuelling. At Addu atoll the Fast Division’s other warships completed refuelling and then sortied to the east very early in the morning of 5 April, with the Slow Division following later in the morning of the same day.

Early on 5 April a Catalina again reported the Japanese carrier fleet, and much the same time Nagumo ordered the launch, under the command of Commander Mitsui Fuchida, of an initial attack force of 53 Nakajima B5N 'Kate' single-engined level bombers and 38 Aichi D3A 'Val' single-engined dive-bombers, escorted by 36 Mitsubishi A6M Reisen 'Zero' single-engined fighters at a point some 345 miles (555 km) to the south-east of Ceylon. Nagumo held back only 45 aircraft on his carriers to cope with any eventualities, and had his staff emphasise to the air crews that there was to be no repetition of the tactical error, now fully appreciated, which the Japanese had made at Pearl Harbor on 7 December 1941 and then at Darwin on 19 February 1942: thus the airmen were to attack the harbour installations and oil tank farms as well as the warships.

The Japanese target was Colombo. The warplanes made landfall near Galle, and then flew to the north along the coast for 30 minutes in full view of those on the ground, but no one informed the RAF at Ratmalana, where the aircraft were still on the ground as the Japanese flew overhead.

The early warning radar at Colombo had provided a first indication of this initial wave of Japanese attack aircraft, but the message was not delivered up the chain of command until 07.40.

In heavy air engagements starting just before 08.00 the Japanese fighters shot down 15 Hurricane and four Fulmar fighters, while losing just seven of their own number, though the British claimed that their anti-aircraft defences had downed 17 aircraft. Six slow Fairey Swordfish single-engined biplane attack bombers, armed with torpedoes, on their way from Trincomalee to Colombo, blundered into the scene and were all shot down, and the Japanese aircraft also destroyed two Catalina flying boats.

One group of Japanese aircraft bombed the shipping in and around the harbour. A second group, attacking at low level with machine gunfire as well as bombs, struck the railway marshalling yards, shops, and the known airfield. Next came higher-altitude level bombers, which aimed for ships and sank the destroyer Tenedos and the 11,198-ton armed merchant cruiser Hector, both of which went to the bottom in the harbour, severely damaged the submarine tender Lucia, and slightly damaged a freighter. The repair facilities were also attacked and destroyed. By 08.35 the raid had ended.

The British immediately sent up Blenheim bombers to counterattack the carriers, but the effort failed.

After recovering its aircraft, the Carrier Strike Force fell back to the south-east.

Away to the west, the Eastern Fleet’s Fast Division had cleared Addu atoll by about 12.00 on 5 April, steaming on a course that would bring it into a position some 290 miles (465 km) to the south of Ceylon at daybreak on 6 April. Somerville also ordered the two heavy cruisers from Colombo to rendezvous with the Fast Division at 16.00 on 5 April, and the two ships thus changed course to make the appointed rendezvous. At 06.48 on 5 April, however, Dorsetshire learned that there were Japanese ships 175 miles (280 km) to the east. Both heavy cruisers went to maximum speed, but their lives were about to end. The visibility was excellent, and shortly after 12.00 the two British ships were located and reported by one of Tone's reconnaissance floatplanes. Nagumo then launched 53 D3A dive-bombers from Akagi, Hiryu and Soryu. Dorsetshire was attacked at 13.38 and, after taking many hits, succumbed at 13.48, while Cornwall sank at about 14.00. Some 424 men of the 1,546 men of the two British ships' crews were killed, and the 1,122 survivors spent many hours in the water before they were rescued by Enterprise and two destroyers.

Although the distance between the Fast Division and the Carrier Strike Force during the afternoon of 5 April was at times no more than 230 miles (370 km), Japanese reconnaissance aircraft failed to find the British ships and Somerville was able to keep out of Japanese range during the day.

Somerville had in fact changed course to the south when he heard of the threat to the heavy cruisers. At 18.17, on receiving confirmation of the sinking of the ships, the British commander ordered the ships of the Fast Division to reverse course and pursue the Japanese force. Search aircraft from Indomitable had failed to locate any Japanese warships, however, and though Somerville wanted to be in position for an attack at daybreak if the carriers were located, reconnaissance through the night failed to yield any result. In the early morning of 6 April, the Slow Division joined the Fast Division.

After sinking the two British cruisers, the Carrier Strike Force withdrew to the south-east. Late in the afternoon, at 16.55 and again at 18.00, on 5 April 1942, two Fairey Albacore single-engined torpedo-bomber and reconnaissance aircraft operating from the British aircraft carriers made contact with the Japanese carriers. One Albacore was shot down and the other damaged before its crew could radio an accurate sighting, thereby frustrating Somerville' s plan for a retaliatory night attack by his radar-equipped Albacore aircraft. Somerville continued to probe for the Japanese carriers during the night of 5/6 April, but his aircraft did not find the Japanese ships and the only British opportunity to launch an attack on the Japanese carriers disappeared.

On the evening of 5 April Ozawa divided his force in order to attack shipping off the Indian coast in what was, with the bombardment of British installations to the south of Calcutta, his primary mission. On 6 April Kurita’s Northern Group, comprising the heavy cruisers Kumano and Suzuya and the destroyer Shirakumo, sank nine ships (including the British 4,921-ton Silksworth, 7,736-ton Autolycus, 9,066-ton Malda and 2,440-ton Shinkuang and the US 4,986-ton Exmoor) off Puri in the Orissa region. Ozawa’s own Central Group, comprising the heavy cruiser Chokai, the light cruiser Yura and the destroyers Asagiri and Yugiri, sank another four ships. Captain Shakao Sakiyama’s Southern Group, comprising the heavy cruisers Mikuma and Mogami, and the destroyer Amagiri, sank three more ships and damaged two others. The light carrier Ryujo, operating with the Central Group, launched air attacks on Vizagapatam and Cocanada, sinking three ships and damaging one other, and also causing civilian panic. The three groups thus sank some 92,000 tons of Allied shipping.

Also on 6 April, Japanese air attack sank the Indian sloop Indus off Akyab island on the western coast of Burma.

Nagumo’s force had continued to the south-east until shortly after 05.00 on 6 April, when it reversed course. By 06.00 on 8 April it was on a north-westerly course, about 520 miles (835 km) due east of its next target, Trincomalee on the north-eastern coast of Ceylon. On this day a Catalina flying boat again reported the return of the Carrier Strike Force but, in the meantime, Somerville has returned with his two battle squadrons to Addu atoll, and instructed the ships at Trincomalee to withdraw to the south.

Again Somerville had wrongly assessed Nagumo’s intentions. Somerville expected an attack on Addu atoll, assuming that Nagumo would expect the Eastern Fleet to return there, and therefore manoeuvred his ships so that he could catch the Japanese carrier fleet with a dawn strike when it neared Addu atoll. This placed the British fleet almost 700 miles (1125 km) from Trincomalee and almost 1,150 miles (1850 km) from the Japanese force. It had thus lost its last chance to engage the Carrier Strike Force.

Appreciating that the Slow Division was more of a liability than an asset, the Admiralty had advised Somerville on 9 April to send it to Mombasa island off the coast of Kenya in East Africa, and Somerville complied. With Nagumo still on the loose, the eastern coast of India itself under bombardment, and with large numbers of freighters being sunk in the Bay of Bengal, the Admiralty had decided for the moment to concede the eastern part of the Indian Ocean to the Japanese, and at 06.00 Somerville ordered the ships of the Fast Division to head for Bombay, on India’s western coast.

As noted above, the light carrier Hermes and her escorts, in Trincomalee harbour, had been ordered to sortie during the night of 8 April on a southerly course, keeping close to the Sinhalese coast. Therefore Hermes, together with the destroyer Vampire, the corvette Hollyhock, the oiler British Sergeant and the depot ship Athelstane, departed the harbour on 9 April.

At 06.00 the Japanese began to launch an attack force of 129 aircraft (91 level bombers and dive-bombers escorted by 38 fighters) from a point some 175 miles (280 km) to the east of Trincomalee. The aircraft struck the naval base at 07.25, and were met in the air by all the British fighters available, namely 17 Hurricane and six Fulmar machines. Since the harbour was empty of ships, the main targets were the naval installations, dockyard and airfield, and in the air battle over Trincomalee the British lost eight Hurricanes and one Fulmar shot down. The Japanese lost five bombers and six fighters, one in an apparent suicide attack on the Trincomalee fuel tanks.

The naval authorities at Trincomalee had been warned at daybreak of the location and number of the raiding ships, and responded with the despatch of nine obsolete Blenheim bombers of the RAF’s No. 11 Squadron. The British aircraft spotted their targets at 10.25, but were immediately tackled by the carriers' protecting fighters. The Blenheim bombers inflicted no damage other than one Japanese fighter shot down in air combat, claiming only three near misses after bombing from an altitude of 11,000 ft (3350 m), for the loss of five of their own number and severe damage to the surviving four.

At the time of the raid Hermes and Vampire were 75 miles (120 km) to the south of Trincomalee. Believing that they could return to Trincomalee once the Japanese raid was over, the ships reversed course at 09.00, and the other ships which had cleared the naval base also began to return.

Hermes had been sighted even before her reverse of course, however, and at 09.00 Nagumo launched 80 dive-bombers and 10 fighters against the British ships. Hermes had no aircraft on board, and was attacked by D3A dive-bombers at 10.35. In a 10-minute pounding the carrier was struck by at least 40 bombs, by 10.50 was dead in the water, and five minutes later capsized and sank with the loss of 307 of her crew. It was then the turn of Vampire: the destroyer lasted 10 minutes before breaking in two and sinking. Hollyhock, British Sergeant and Athelstane all suffered the same fate, but the hospital ship Vita was spared, and later rescued 590 survivors.

Apart from the warships they had sunk, the Japanese forces had also sunk 23 merchant ships totalling 112,312 tons, and Nagumo now turned his fleet toward home, for his carriers had been at sea constantly since 26 November 1941, and required a thorough overhaul. Nagumo also appreciated that his crews needed rest, and that his carriers' air groups needed replacement pilots and crews. At the time, moreover, the Imperial General Headquarters had no further task in mind for the Carrier Strike Force and recalled it to Singapore. Reinforced by the 3^rd Destroyer Flotilla, Ozawa passed through the Strait of Malacca on 9/10 April, followed by Nagumo on 12/13 April.

At the same time the Fast Division proceeded on 9 April to Bombay and the Slow Division to Kilindini on the East African coast.

The Japanese submarines operating to the west of India, in the Maldive and Laccadive passages, and to the west of Ceylon, also enjoyed success: I-2 sank one unidentified ship, I-3 sank one 5,051-ton ship and damaged one 4,872-ton ship, I-5 sank one 6,617-ton ship and a sailing vessel, I-6 sank two ships totalling 11,321 tons as well as two sailing vessels, and I-7 sank one 9,415-ton ship.

Thus Nagumo returned, having won spectacular victories at Pearl Harbor, Rabaul, Port Darwin, and finally Colombo and Trincomalee, all at the cost of a mere handful of aircraft and crews. In four months of raiding, not one of his ships had received even a single hit. The Eastern Fleet had been driven from the Indian Ocean to the coast of East Africa, however, and the Japanese seizures of Burma, the Andaman and Nicobar island groups, and Sumatra were thus shielded from British naval intervention.

An added bonus for the Japanese was that there was, of course, for several months a major reduction in the flow of ships sailing independently in the Indian Ocean. At the same time, the Japanese effort had further strengthened the westernmost portion of its defence perimeter, from Burma to Singapore.

In overall terms, 'C' (ii) had demonstrated the Japanese superiority in carrier operations and also exposed the poor capabilities of the RAF in the Far East, but it did not destroy British naval power in the Indian Ocean. It is arguable that, by making full use of signal intercepts, decryption, reconnaissance and superior radar, Somerville had been able to save his two fleet carriers, Formidable and Indomitable, to fight another day. However, it might equally be said that the mistakes made by the Royal Navy meant that the main fleet from Addu atoll was unable to make contact with the Carrier Strike Force as had been intended.

An invasion was feared by the British, who interpreted the Japanese failure to do so as the result of the heavy Japanese losses over Ceylon. However, the reality of the situation was that the Japanese lacked the manpower, shipping capacity and land-based air power which would have been required for an amphibious invasion and occupation of Ceylon, and were not even in a position to make a temporary occupation as a raid. Ceylon did not face a real threat of invasion at any point during the war.

Ceylon was of great strategic importance as it commanded the Indian Ocean, and thus controlled access to India, the vital Allied shipping routes to the Middle East, and the oilfields of the Persian Gulf. Ceylon also held most of the British empire’s surviving resources of rubber. An important harbour and naval base, Trincomalee, was located on the island’s eastern coast. Japanese propaganda had an effect on much of the Sinhalese population, who now awaited their arrival.

The raid had allowed the Japanese navy to prove its current mastery of the Indian Ocean and Bay of Bengal, and its ability to seize territory by capturing the Andaman islands group.

Despite its losses, the British fleet escaped further short-term conflict by withdrawing. In view of the currently overwhelming Japanese naval superiority, especially in carrier operations, this can be seen only as a wise decision. The Japanese had already planned to establish a submarine base on the island of Madagascar for a campaign against Allied shipping off the east coast of Africa, and now a weakened Ceylon invited invasion, possibly with limited objectives, such as the seizure of Trincomalee, for the creation of a more convenient base.

That the British expected an invasion seems to be substantiated by a speed made by Layton in mid-April in which he told his audience of personnel of the damaged airfield outside Trincomalee that the Japanese had 'retired to Singapore, to refuel and rearm, and to organise an invasion force, which we think is coming back to attack us'.

The British army sent three divisions to strengthen Ceylon’s defences against the threat of invasion and also any anti-British rising. Ceylon later become an important base for the planned 'Zipper' operation to retake Malaya and Singapore.