Main Covering Force (Nagumo).
Aircraft-carriers.
Akagi (Akagi class).
Hiryu (Hiryu class).
Soryu (Soryu class).
Shokaku (Shokaku class).
Zuikaku (Shokaku class).
Fast Battleships.
Haruna
Hiei
Kirishima.
Kongo. (all Kongo class)
Cruisers.
Abakuma (Nagara class).
Chikuma (Tone class)
Tone (Tone class).
Destroyers.
Akigumo (Yugumo class).
Arare (Asashio class).
Hagikaze (Kagero class).
Hamakaze (Kagero class).
Isokaze (Kagero class).
Kagero (Kagero class).
Kasumi (Asashio class).
Maikaze (Kagero class).
Shiranuhi (Kagero class).
Tanikaze (Kagero class).
Urakaze (Kagero class).
Bay of Bengal Raid Force (Ozawa).
Light Aircraft-carrier.
Ryujo (Ryujo class).
Cruisers.
Kumano (Mogami class).
Mikuma (Mogami class).
Mogami (Mogami class).
Sendai (Sendai class).
Suzuya (Mogami class).
Takao (Takao class).
Yura (Nagara class).
Destroyers.
Amagiri
Asigiri
Ayanami
Fubuki
Hatsuyuki
Isonami
Murakumo
Shikinami
Shirayuki
Uranami
Yugiri (All Fubuki class).
Ryujo carried about fifteen “Kates” and twenty of the older “Claude” fighters. In addition, all of the Japanese battleships and cruisers carried one or two “Dave” or “Jake” seaplanes, which were widely used for spotting purposes. The reconnaissance effort was further supplemented by long range “Mavis” seaplanes operating from an advance base at Port Blair.
Several submarines were also operating in the Bay of Bengal, the west coast of India, and the areas south and east of Ceylon.
Analysis.
Overall, although the two sides had roughly equal numbers of ships, the Japanese force had a big tonnage advantage. They also had a big qualitative edge. Their fleet was far more modern, far more coherent, and far better suited to the new style of carrier warfare.
In the air the position for the British was even worse. Even with all their land-based aircraft they were still heavily outnumbered, fielding less than 250 planes against nearly 400. In addition the Japanese aircraft were almost uniformly faster, more maneuverable and better-armed. Their biggest advantage was in having a much longer reach. Most of the British aircraft were of very low endurance.
The British also had insufficient information about the capabilities and intentions of their opponents. They had only an approximate date for the attack and no idea at all what force the Japanese would utilise, only that it would be superior to their own. The British Admiralty had decreed that it was vital that a "fleet in being" be retained in the Indian Ocean in order to provide any kind of security at all to the Indian sub-continent. Therefore, if all the Japanese planned was a raid, Somerville's purpose would be to keep his fleet from becoming entangled with a vastly superior force. On the other hand, if the Japanese incursion was a prelude to a full scale invasion of Ceylon, then he would have to make the utmost effort to protect the island, even if it meant losing the entire fleet. If he had known that the Japanese had decided to use their main carrier strike force Somerville would certainly have withdrawn as quickly as possible. As it was, he was unable to because of the potential threat to Ceylon.
It was a painful dilemma to be in and Somerville had no illusions about his task. He quickly realised his only chance was an air strike at night from his carriers, possibly in conjunction with land-based aircraft, which hopefully would weaken the enemy enough to enable successful engagement with his capital ships. It was a long shot against a wary opponent, and Somerville was fully aware that it was not likely to work.
The course of the sweep, 1st—9th April, 1942.
Somerville arranged for land-based air patrols to be conducted south-east of Ceylon to cover the anticipated Japanese approach path. By the night of 31st March the Eastern fleet was concentrated eighty miles south of the island in an intercept position. Somerville's plan was to locate and track the Japanese fleet quickly whilst staying out of their air reconnaissance range until nightfall, then to steer to a launching position as fast as possible.
Accordingly, flying constant patrols, the Eastern fleet swept different areas to the south and east of Ceylon for three successive nights, but failed to sight any Japanese ships. The longer-ranged Catalina patrols from Ceylon, ordered to search to a depth of 420 miles, similarly reported no contact.
Somerville's problems began to stack up. He had to consider the quite likely possibility that Intelligence had been wrong about the timing of the Japanese attack, or even its very existence. Continually operating south of Ceylon was increasing the chance of detection by Japanese submarines, which were known to be operating in the area. The fleet oiler Appleleaf had replenished some of the destroyers on 2nd April, but other supplies were already running low, owing to a general lack of supply ships and tankers. The "R" class battleships of the 3rd Battle squadron in particular were running acutely short of water. In addition, the ever present demand for ships for other duties was becoming pressing. Convoys were assembling at Ceylon and would need escorts. The threat to India had prompted the war cabinet in London to undertake the emergency countermeasure of invading Madagascar and warships would soon be needed to both execute and cover the landings.
Faced with all this, Somerville decided to abort the operation and begin reallocating ships to other duties. His decision to do so was strictly speaking premature, for it was not based on definite information. In retrospect, it may have saved the Eastern fleet from complete disaster.
The dispersal of the fleet began on the 3rd April. Dorsetshire was detached to Colombo to resume a refit. Cornwall was similarly detached to the same port in order to escort a convoy. The destroyer Decoy had already been sent to Colombo for repairs on the 1st following a break down in her main feed pump. Hermes and the Australian destroyer Vampire were sent to Trincomalee to prepare for the Madagascar operation. The destroyer Fortune was sent to the aid of the merchant ship Glenn Sheil, which had been torpedoed by a Japanese submarine. The rest of the fleet returned to Addu Atol. Force "A" arrived at 1200 hours on the 4th of April and commenced refuelling immediately. Force "B" arrived three hours later.
The British force was therefore badly scattered when a Catalina detected large numbers of Japanese ships about 360 miles south-east of the southern tip of Ceylon at 1600 hours the same day. The attack (as at Pearl Harbour) had been timed to coincide with a national holiday, (in this case Easter Sunday on the 5th of April) and not on the 1st at all.
Somerville had been caught off-guard. The Eastern fleet would need at least another 24 hours to complete fuelling, and could not possibly intercept the Japanese before they could attack Ceylon. He therefore decided to concentrate his refuelling efforts on the fast division alone and sailing them as quickly as possible, ordering the slow division to follow on later. Meanwhile, air defences at Ceylon were alerted, and all shipping capable of sailing in Colombo harbour was ordered to disperse to the westward. Dorsetshire and Cornwall were instructed to rejoin the fleet with all despatch, and Hermes and Vampire, which had reached Trincomalee, to hurriedly refuel.
At 0800 on 5th April ninety-one Japanese dive-bombers, escorted by thirty-six fighters, attacked Colombo harbour and Ratamalana airstrip. The newly installed radar system broke down, and though all the defending fighters were able to take off they were caught at low altitude by the raid's escorts. No less than nineteen were shot down, and the Japanese were able to pre
ss home their attacks. Their dive-bombing was very accurate, but thanks to the prudent decision to evacuate the harbour little actual damage was done. The destroyer Tenedos, which had been under repair, was sunk at her moorings, as was the armed merchant cruiser Hector. Harbour facilities were badly damaged, and No 788 squadron in transit from Trincomalee blundered into the dogfights and all six of its Swordfish were lost. The Ceylon air defences counter-attacked with their land-based bombers, but the weather had by then closed in and the Blenheims failed to make contact.
The following day found the British still desperately trying to concentrate. Force “A” was closing on the reported position of the Japanese fleet, but could not possibly engage without the support of Force “B”. The weather was fair, almost dead calm with near perfect visibility, and Japanese reconnaissance planes had no difficulty in detecting Dorsetshire and Cornwall as they steamed to rejoin. Several shadowing reports were sent on to the flagship, but none were picked up. At around 1340 a force of over fifty dive-bombers caught up with the two cruisers. For some reason radar failed to give warning of the incoming strike, but when three aircraft were spotted at high altitude Dorsetshire opened fire immediately. These planes promptly dived on Cornwall, scoring a bomb hit on her hangar. Whilst Dorsetshire was firing on this first group, another formation of three attacked her. In spite of wild avoiding action to starboard, all three bombs hit, disabling the radios, the steering gear and most of the port side AA guns. The Japanese continued to attack in successive formations of three. In just four minutes Dorsetshire took at least another six direct hits and began to list heavily to port. The order to abandon ship was given, and only two or three minutes later she capsized and sank stern first.
Cornwall fared little better. She took at least eight direct hits and a great many near misses, which did tremendous damage underwater, including causing the engine and boiler rooms to flood. She was abandoned at 1355 and sank bow first five minutes later. The survivors numbered nearly 1200 and were to remain adrift in the shark infested sea for some thirty hours. Although they were only eighty miles from rendezvousing with the rest of Force “A”, tactical considerations delayed rescue efforts.
Throughout the 5th April, Catalinas continued to give shadowing reports of Japanese heavy units (although two were intercepted and shot down). Initially these movements seemed to indicate that an air attack on Addu Atol was about to be made, and Force “A” changed course to keep to the south of the estimated Japanese position. The British now believed that they were heading west-southwest parallel to their opponents. It was only at 1800 that it was realised that the Japanese had turned to the northwest about an hour previously. Somerville immediately turned Force A to the northwest as well in order to avoid Japanese search patterns, unite his forces, and yet remain close enough to launch a night air strike.
His manoeuvring was successful. The Eastern fleet remained undetected and closed to within strike range of the Japanese by nightfall. From 1930 until 0600 the following morning, torpedo-laden British aircraft probed northwards to a depth of 200 miles, but the only contact made was with Force B, which rejoined at 0900. Somerville's forces were now united, but the exact position of the Japanese had been lost. To be caught in the open during daylight hours was to court disaster. The Eastern fleet would have to retreat. Still fearing an attack on Addu Atol, Somerville resolved to keep well clear of the place. He headed eastward, detached Enterprise, Paladin and Panther to pick up survivors from Cornwall and Dorsetshire, and awaited the chance for another night attack.
However, no definite reports of the position of the enemy were made. Still concerned for Addu Atol, the Eastern fleet cautiously took a circuitous route back to the base via the Veimandu Channel, flying constant all-round air searches. They arrived at 1100 on the 8th of April and immediately commenced refuelling.
The Japanese, who were unaware of the secret base at the Addu Atol, had been leisurely heading northwards. They had been disappointed by the paucity of targets at Colombo and hoped for better results at Trincomalee. A Catalina spotted them on the afternoon of 8th April, and shipping in Trincomalee harbour, including Hermes, was ordered to disperse southward.
At 0700 the next morning radar detected large numbers of aircraft about ninety miles off, and 25 minutes later both level and dive-bombing attacks were made against the docks and the airbase. As at Colombo the bombing was extremely accurate. Considerable damage was done to the yards and also to the airbase, a dozen planes in various stages of assembly being destroyed on the ground. The British again riposted with their level bombers, and this time managed to locate the Japanese fleet -- and swarms of defending fighters. Gritting their teeth the British pressed home the attack, but no hits were scored. In contrast all nine Blenheims on the raid were badly shot up, and five failed to make it back.
Subsequently, Japanese reconnaissance planes returning from a patrol over Colombo detected Hermes and her escorts as they made their way back to Trincomalee. The sighting report they made was picked up and decoded by British Intelligence, and fighters were swiftly ordered to cover the carrier. Unfortunately the recent air raid at Trincomalee had badly disrupted communications and the message (and subsequent assistance) was delayed.
At least eighty-five Japanese planes smothered the hapless Hermes with more than forty direct bomb hits in the space of only a quarter of an hour. The Japanese force then went on to sink Vampire, the corvette Hollyhock, and two auxiliaries. They did however respect the conventions of war and avoided attacking the hospital ship Vita, which was able to pick up most of the survivors.
Meanwhile Somerville had come to the correct conclusion that the Eastern fleet was not strong enough to dispute control of the area with the Japanese. Accordingly, with the approval of the British Admiralty, he ordered Force B to Kilindini in East Africa for training, while Force A sailed for Bombay. Ceylon would have to fend for itself.
But the island's paltry defences were not to be tried again. On the afternoon of 9th April the Japanese force was spotted for the last time. They were 170 miles from Ceylon and heading south at high speed. The Indian Ocean sweep was over.
Casualties.
Total British naval losses amounted to one light carrier, two eight inch gun heavy cruisers, two destroyers, and several minor vessels. In addition Ozawa's raid force had romped around the Bay of Bengal doing tremendous damage to the merchant shipping there and also launching air strikes on Vitagapatan and Cocanada. All told, Japanese aircraft had sunk fifteen vessels, and Japanese cruisers another eight. Six more merchants were lost to submarines either in the Bay of Bengal or on the west coast of India for a grand total during the period of dearly 150,000 gross tonnage. Sea communications to Calcutta were badly disrupted, a particularly serious blow as the port was the main staging area for reinforcements to the Burma front. In contrast no Japanese ships were sunk, in fact none were damaged in any way at all.
Aircraft casualties are more difficult to estimate, in the face of incomplete reports and conflicting propaganda. Overall it seems likely that the assorted air operations between the 2nd and 9th of April cost the British about forty planes, with another dozen partially assembled machines being lost on the ground during the attack on China Bay. The Japanese probably lost about half that.
Personnel casualties are also difficult to appraise accurately. Japanese losses were confined exclusively to aircrew and were therefore fairly minimal. The sinking of Dorsetshire and Cornwall claimed more than 420 lives, the sinking of Hermes, Vampire and the various auxiliaries with them over 350. Adding aircrew, merchant ship crews and victims of the bombing of Ceylon brings total British casualties to well over 1000, almost all of them military.
Conclusions.
1) The British policy of defending the Far East with large obsolete forces was once again shown to be inadequate. In fact, rather than acting as a deterrent, the presence of the Eastern fleet was a positive inducement for the Japanese to attack, in order to eliminate a potential threat.
2) The dominance of aircraft-carriers at sea was confirmed. At no time did any of the battleships involved sight enemy warships, nor did any of them fire a shot in anger.
3) Japanese reconnaissance, largely carried out by seaplanes from their cruisers and battleships, was distinctly lacklustre. Although they located Hermes, Dorsetshire and Cornwall, not once was the main body of the Eastern fleet spotted. Also no attempt was made to find the large numbers of merchant vessels that had scattered from both Trincomalee and Colombo. In contrast, the allied reconnaissance effort, spearheaded by the excellent Catalina, performed quite admirably given the limited numbers available.
4) All British witnesses comment on the outstanding accuracy of Japanese dive-bombing attacks. The high quality of both their aircraft and crews was a major factor in Japan's early war successes.
5) The Japanese took great care to limit attacks to military targets only. In spite (or perhaps because) of this, the morale effect of the sweep on the civilian population was considerable. Invasion scares started throughout India and took some time to die down.
6) The British learned from defeat. Air reinforcements to Ceylon and the Far East in general were urgently dispatched. However, apart from periodic sorties to suppress Axis light forces, there was no further naval activity in the Indian Ocean.
Appendix—British Aircraft deployment, 4th April 1942.
The Japanese Sweep Into the Indian Ocean Page 2