Imperial Japanese Navy Begins Sustained Attacks on Allied Forces in the Indian Ocean
Following the destruction of the American-British-Dutch-Australian Command forces in the battles around Java in February and March, the Japanese sortied into the Indian Ocean to destroy British seapower there and support the invasion of Burma.
The Japanese force, commanded by Admiral Chuichi Nagumo, had six carriers: Akagi, Ryūjō, Hiryū, Sōryū, Shōkaku, and Zuikaku. This powerful force left Staring Bay, Celebes on 26 March 1942.
Signal decrypts provided the British commander of the Eastern Fleet, Vice Admiral Sir James Somerville with warning of the Japanese sortie, and he retreated to Addu Atoll in the Maldive Islands, expecting an attack on 1 or 2 April.
The first raids were against shipping in the Bay of Bengal by the carrier Ryūjō and six cruisers under the command of Admiral Jisaburo Ozawa. They sank 23 ships. Five more were sunk by submarines off India's west coast.
When the expected attack on Ceylon failed to take place, Somerville sent the slow carrier Hermes back to Trincomalee for repairs, escorted by the heavy cruisers Cornwall and Dorsetshire, and the Australian destroyer HMAS Vampire.
On the evening of 4 April, the Japanese fleet was detected 400 miles south of Ceylon by a PBY Catalina flown by Squadron Leader Leonard Birchall of 413 Squadron, Royal Canadian Air Force. The location of the fleet was transmitted before the Catalina was shot down by a Zero fighter from the Hiryū.
Using much the same tactics and carriers that had been so successful in the Pearl Harbor attack, early in 1942, the Japanese Navy went after the British Fleet's major anchorage in the Indian Ocean. But thanks to Japan's obsession to strike at American-held Midway Island in the central Pacific, a victory of equal magnitude to that enjoyed over America's Pacific Fleet was denied the Japanese planners