A converted German auxiliary cruiser and merchant raider Atlantis captured and scuttled Automedon in 1940 in the Indian Ocean.

Like most members of the class, she was powered by two steam turbines, which drove a single screw via double reduction gearing.

[7] In 1934 Automedon's code letters KNQG[8] were superseded by the call sign GBZR, and she was fitted with wireless direction finding.

[10] On 31 March 1940 Automedon left Liverpool for Australia, but this time sailed via Freetown in Sierra Leone and Durban in South Africa.

[citation needed] At about 0700 hrs on 11 November 1940, the German auxiliary cruiser Atlantis intercepted Automedon about 250 nautical miles (460 km) northwest of Sumatra, approaching on a heading that would bring the two ships close together.

Ulrich Mohr of Atlantis later said Automedon was in the worst condition he had ever seen; the close-range shelling had destroyed virtually every structure above the hull, and nothing was left undamaged.

A thorough search of Automedon found 15 bags of top secret mail for the British Far East Command, including a large quantity of decoding tables, Fleet orders, gunnery instructions, and Naval Intelligence reports.

Marked "Highly Confidential" and equipped with holes to help it to sink if it had to be thrown overboard, the bag contained an envelope addressed to Robert Brooke Popham, Commander-in-Chief of the British Far East Command.

The envelope contained documents prepared by the British War Cabinet's Planning Division which included their evaluations of the strength and status of British land and naval forces in the Far East, a detailed report on Singapore's defences, and information on the roles to be played by Australian and New Zealand forces in the Far East in the event that Japan entered the war on the Axis side.

[12][13] Captain Bernhard Rogge of Atlantis set a time limit of three hours in which 31 British and 56 Chinese crewmen, three passengers, their possessions, all the frozen meat and food and the ship's papers and bags of mail were transferred.

He was concerned as another ship observing the two stationary vessels would quickly guess what was happening and send a radio message before Atlantis could take any action.