The Air raid on Ceylon (5 April 1942) also known as the Easter Sunday raid, was an air attack on Colombo, British Ceylon (now Sri Lanka) by Imperial Japanese Navy aircraft from the aircraft carriers of the 1st Air Fleet () during the Indian Ocean raid (31 March – 10 April 1942). The Japanese plan was to destroy the British Eastern Fleet in harbour.

The British received warning of the raid in March through decoded Japanese wireless messages and from air reconnaissance. The British forestalled the Japanese by dispersing shipping from the harbours in Ceylon before the attack. The Japanese aircraft were met by fighters of 222 Group, Royal Air Force, the Fleet Air Arm (FAA) of the Royal Navy and anti-aircraft guns.

Port facilities were damaged and ships in Colombo harbour were sunk or damaged. The bulk of the Eastern Fleet was not found and survived but several ships were sunk at sea after the raid. The Eastern Fleet moved temporarily to East Africa, from where it sent carrier forces into the central and eastern Indian Ocean. The Japanese Navy was unable to repeat the raid because of its commitments in the Pacific.

Background

British Ceylon (Sri Lanka)

Ceylon (now Sri Lanka) is off the south-east of India between shipping routes from Singapore and Rangoon to the Red Sea and the Persian Gulf. There are natural harbours at Colombo on the south-western coast and Trincomalee on the north-eastern coast, a naval anchorage and base. Ceylon was a geographically important part of the British Empire and its system of trade, communication and military organisation. In the 1930s more shipping tonnage was handled in Ceylon than all the ports of India. Since the beginning of the Second World War, the colonial government had engaged in mass recruitment for local defence, overseas labouring and expanded food production. Tea and rubber production was emphasised and rubber output rose from in 1941 to in 1943. The 3,600 workers in civil engineering converted to the repair and refitting of ships and the manufacture of dummy aircraft, guns and radar installations.

When the Pacific War began on 7 December 1941, the Allied disasters in the Pacific, Malaya and the British débâcle at the Battle of Singapore in February 1942 made Colombo Harbour the basis for eastern trade and the centre for the assembly of Indian Ocean convoys. Colombo port was large enough for 45 ships but soon had 100 to 110 ships at once, causing much overcrowding. The strategic importance of Ceylon increased and British planners deemed the island essential to the defence of India and Allied lines of communication through the Indian Ocean. The Allied defeat in the Dutch East Indies campaign (11 January – 9 March 1942) left the Indian Ocean vulnerable to Japanese attacks. The Malacca Strait in the Netherlands East Indies was about east of Trincomalee, making it a useful base for attacks on Japanese ships sailing to Rangoon in Burma.

From September to December 1941, 710 troop reinforcements arrived on the island and from January to March 1942, another 2,612 arrived; during April and June, 2,112 more troops joined the garrison (2,872) and 4,993 troops moved between the Far East and Ceylon from October 1941 to March 1942. The extent of the disasters that befell the British in early 1942, led in March to Admiral Sir Geoffrey Layton being transferred from the temporary command of the Eastern Fleet and installed as the Commander-in-Chief, Ceylon, after Admiral James Somerville arrived to command the fleet. Layton was given authority over the military forces on the island and the civilian authorities of the governor, Sir Andrew Caldecott, "Do not ask permission to do things. Do them and report afterwards what you have done". Layton found the same complacency and inertia in Ceylon as he had experienced in Malaya,

Air defence

In September 1941 the Royal Air Force (RAF) had established No. 222 Group RAF (Air Vice-Marshal John D'Albiac) on the island in command of 273 Squadron at China Bay airfield with four Vickers Vildebeest and four Fairey Seal torpedo bombers. Until February 1942, the air defence of Ceylon had been a Royal Navy responsibility and 803 Naval Air Squadron (803 NAS) and 806 Naval Air Squadron (806 NAS) had transferred to Ceylon from the Middle East, six Fairey Fulmars at a time. Eight Hurricanes that had been assembled at Karachi, were flown to Ceylon, six of the Hurricanes, ferried to Ceylon by pilots of 136 Squadron, arrived at RAF Ratmalana on 23 February. The Torpedo Bomber Reconnaissance Pool, 788 Naval Air Squadron (788 NAS) with six Fairey Swordfish for the Eastern Fleet, was formed on 18 January at China Bay, near Trincomalee and was pressed into service in defence of Ceylon.

By March 1942, there were airfields at China Bay near Trincomalee, Ratmalana near Colombo, an airstrip was built at the Colombo Racecourse to relieve congestion at Ratmalana and another airstrip had been built at Minneriya on the south coast. China Bay was a grass landing ground that had the sea at both ends and there was a ridge along the southern edge; a low ridge ran along the northern boundary. Aircraft could only land and take off to the north-east or south-west, depending on the wind direction. There were fuel storage tanks beyond the north-east corner of the airfield at the Royal Naval Base Trincomalee. Anti-aircraft defence comprised four obsolescent QF 3-inch 20 cwt anti-aircraft guns at Trincomalee. The danger of an air attack by aircraft of the Japanese Navy aircraft carriers was acute after the examples of the Attack on Pearl Harbor in December 1941 and the Bombing of Darwin in February 1942. The airfields at Ratmalana, near Colombo and China Bay had been expanded.

On 6 and 7 March the aircraft carrier dispatched sixty Hurricanes of 30 Squadron and 261 Squadron, that had been intended for Java. On 30 March, the RAF reconstituted 258 Squadron that had been mauled in the fighting in British Malaya, Sumatra and Java. By 4 April, 803 NAS and 806 NAS of the Fleet Air Arm were ready with 24 Fulmars; the ground defences had been reinforced to 144 anti-aircraft guns. On 5 April, there were 37–38 serviceable Hurricanes near Colombo.

The first Consolidated PBY Catalina long-range flying boat of 413 Squadron Royal Canadian Air Force (RCAF) arrived on 28 March, with the ground crews following on by sea, two more arrived before the raid and on 6 and 7 April two more Canadian Catalinas arrived. By 4 April, four 205 Squadron RAF Catalinas had reached the island. There was one operational Dutch Catalina of the Netherlands Naval Aviation Service (MLD); two of the RAF and three Dutch Catalinas were unserviceable. The Catalinas were based at Koggala lagoon, at the south end of the island.

Radar

Radar stations, code-named Air Ministry Experimental Stations (AMES) were established at the Royal Colombo Golf Club at Ridgeway about north of Ratmalana airfield (AMES 254) and at Trincomalee (AMES 272). AMES 254 personnel arrived on 18 March and the equipment four days later. AMES 254 became operational on 25 March and was linked by telephone to 20 Operations Room on 28 March. The terrain around the radar limited maximum range to and the altitude of an object affected the detection range. The short notice may not have been sufficient for operators to tell the difference between false radar echoes produced by local conditions and real ones. The aerial projected "lobes" in which objects might be detected, with gaps between some lobes or lobes overlapping. The distance travelled by an aircraft between the maximum range of AMES 254 to Ratmalana was A Zero took about 17 minutes to cover the distance and it took a Hurricane five minutes to take off and six more to climb to interception altitude. There were only six minutes for AMES 254 to report to 20 Operations Room and for orders to be issued if pilots were going to avoid being caught climbing.

Japanese preparations

On 9 March 1942 the Japanese Combined Fleet (Admiral Chūichi Nagumo) was ordered to protect Japanese sea communications from attack by the British army in Burma and to "sweep the Bay of Bengal clear of British naval units", ready for the occupation of the Andaman Islands and the Nicobar Islands in the eastern Indian Ocean. In February 1942, the Japanese army and navy conducted a war game to examine an invasion of Ceylon but both services were lukewarm. The army did not have the troops for an invasion and occupation; the navy was preoccupied with its operations in the Pacific.

There were insufficient ships to shift an invasion force and supply a garrison against attacks by British ships, submarines and aircraft. The Prime Minister, Hideki Tojo, rejected the plan indefinitely. By 16 March, the plan for an Indian Ocean raid was to depart from Staring Bay in the Celebes (now Sulawesi) in the Netherlands East Indies on 26 March, ready to attack Colombo on 5 April (C day). The Combined Fleet was based on the five aircraft carriers of the 1st Air Fleet, comprising of the 1st Carrier Squadron, and of the 2nd Carrier Squadron, with and of the 5th Carrier Squadron.

British code-breaking On 4 December 1941 the Japanese had altered their code JN-25B that prevented British code-breakers of the Far East Combined Bureau (FECB) since 1936, a station of the Government Code and Cypher School (GC&CS) at Bletchley Park in England. from reading Japanese wireless messages. On 3 March 1942, the British began reading JN-25B messages again. By the middle of the month, decrypts revealed that the 1st Carrier Squadron and the 2nd Carrier Squadron were at Staring Bay in the Celebes, an Imperial Japanese Navy fuelling base and that the 5th Carrier Squadron was en route. Around 20 March decrypts revealed that a carrier force in Area D was going to attack DG on 2 April (C Day). On 28 March it was inferred that DG was Colombo. Japanese preparations were delayed by the late arrival of the 5th Carrier Squadron at Staring Bay on 24 March and the fleet sailed on 26 March.

The British air defences in Ceylon were alerted for an attack on 1 or 2 March and merchant shipping dispersed from Colombo. The Eastern Fleet sortied on 30 March to patrol south of the island. Aerial reconnaissance by Catalina flying-boats concentrated on the south-east, the right direction that the Japanese would approach but with no sightings, the Eastern Fleet retired late on 2 April toward Addu Atoll to refuel at Gan (Port T) about south-west of Ceylon. The heavy cruisers and sailed for Colombo and set out for Trincomalee to resume their commitments.

Prelude

2−4 April

During the morning of 2 April, three Kawanishi H6K flying boats from Port Blair made a reconnaissance flight towards Ceylon and early on 4 April, an H6K was sent to Trincomalee, observing eight merchant ships and a destroyer in the harbour. The Japanese cancelled a planned reconnaissance of Colombo harbour on 4 April by cruiser floatplanes. Before dawn on 4 April, Catalina QL-A of 413 Squadron RCAF, flown by Squadron Leader Leonard Birchall, took off from Koggala to reconnoitre the southern-most patrol sector.

Later in the day, the crew decided to repeat a leg that took them to the southern-most point of their patrol. At 16:00, the crew spotted the Japanese fleet on the southern horizon, about south-east of Ceylon. Three Zeros from Akagi, three from Zuikaku and six from Hiryū attacked the Catalina as it closed to get an accurate sighting. The radio was destroyed mid-transmission and only the sighting not the size of the fleet was received at Ceylon; several minutes after the Zeros attack began, QL-A was forced down on the sea.