In the spring of 1942, the Japanese naval juggernaut appeared unstoppable. The U.S. Navy was on the strategic defensive in the Pacific, and with the ABDA (American, British, Dutch, Australian) fleet destroyed in the Battle of the Java Sea, the only remaining Allied naval force of any significance in the region that might counter Imperial Japanese Navy (IJN) aggression was the Royal Navy’s 29-ship Eastern Fleet under the command of Vice Adm. James Somerville.

In late March, the IJN’s Southern Force, containing three fleets (Malayan, submarine, and First Air) under the overall command of Vice Adm. Nobutake Kondo, entered the Bay of Bengal. Its three-fold mission was to support the Japanese Army offensive in Burma, sink Allied shipping, and most important of all, eliminate the Eastern Fleet.

“The most dangerous moment of the war, and the one which caused me the greatest alarm, was when the Japanese fleet was heading for Ceylon and the naval base there. The capture of Ceylon, the consequent control of the Indian Ocean, and the possibility at the same time of a German conquest of Egypt would have closed the ring and the future would have been black.” – Prime Minister Winston Churchill

The Malayan Fleet, under Vice Adm. Jisaburō Ozawa struck first. After supporting the amphibious assault of the Andaman Islands (conquered in one day and without a shot being fired), Ozawa continued west, sinking any vessel he found. On April 6, he launched air strikes on two ports on India’s east coast, ultimately sinking 23 ships and damaging numerous facilities before retiring.
The Japanese submarine fleet patrolled India’s west coast, conducted reconnaissance, and sank allied shipping. One submarine, the I-10, traveled as far west as Madagascar, sank nine merchant ships, and damaged the battleship HMS Ramilles during its four-month patrol.

The task of eliminating the Eastern Fleet, code named Operation C, was given to the First Air Fleet and its carrier strike force, Kido Butai (Mobile Unit/Strike Force) under the command of the hero of Pearl Harbor, Vice Adm. Chuichi Nagumo and containing the heavy carriers Akagi, Hiryu, Soryu, Shokaku, and Zuikaku, with more than 300 aircraft and supported by four battleships, seven cruisers, and 19 destroyers.

An RCAF Catalina patrol plane spotted Nagumo’s force on April 4. Its crew successfully transmitted the fleet’s location before being shot down. Despite this warning, the RAF was caught unprepared – with its pilots eating breakfast when Japanese aircraft arrived in the skies over the port of Colombo the next day at dawn. Incredibly, the British radar stations were unmanned that morning. Among the reasons later given were that April 5 was both a Sunday and a holiday (Easter), and that the stations were shut down for routine maintenance.

Nagumo had hoped to catch Somerville’s fleet in the same way his pilots had found the U.S. Navy fleet at Pearl Harbor. But the British had cracked the IJN naval code, so Somerville knew Nagumo’s plans. Because Somerville had been ordered to save his fleet even if it meant losing Ceylon, he had sent most of his ships south to Addu Atoll, a small refueling base in the Maldives about 600 miles southwest of Ceylon. The Japanese air raid found only two ships – an auxiliary cruiser and an old destroyer – at the harbor of Colombo. These were quickly sunk. Japanese pilots bombed facilities and airfields, and shot down at least 27 British aircraft. A second Japanese attack wave found and sank the British cruisers Cornwall and Dorsetshire.

On April 9, Nagumo launched a raid against British air and naval installations in and around Trincomalee harbor on Ceylon’s northeast coast, sinking the light carrier HMS Hermes, the Australian destroyer HMAS Vampire, and the corvette HMS Hollyhock, shooting down a number of aircraft and damaging harbor facilities. On April 12, Nagumo’s fleet, having been at sea since late November 1941, retired to rest and refit, having lost less than 30 aircraft.

British forces braced themselves for an invasion of Ceylon. But that was never a part of the IJN’s plan. Its ultimate objective was the Vichy-ruled island of Madagascar, where the IJN wanted to establish a long-range submarine base and cut the Allied shipping lanes to Egypt, the Soviet Union (through the Persian Gulf), and India. But that didn’t happen, either.

On April 18, the Doolittle Raid struck the Japanese home islands, shocking the nation and forcing the IJN high command to recall Nagumo’s fleet for a showdown with the U.S. Navy at Midway.