http://www.nesa.org.uk/html/automedon-ultra.htm

A complete Set of current Naval ciphers was seized from the submarine HMS Seal, captured off the German coast in 1940. There is still some mystery surrounding this incident, because nearly an hour passed between the submarine being forced to the surface and surrendering, yet no attempt was made to throw the ciphers overboard. On 11th September 1942 a motor torpedo boat was captured by the Germans which again carried valuable cipher material, similar secret Naval documents were found in Royal Naval vessels lost off Crete.


One or their early successes was the capture by the raider Atlantis (on 11 July 1940), of the steamer City of’ Baghdad. from which was taken current copiesof the Merchant Navy cipher and secret call-signs that enabled the captain of the Atlantis, Bernhard Rogge, to read messages for other Allied merchant shipping, plot their likely course, and intercept them without difficulty. On several occasions prisoners were told by the Germans the name of the vessel they would intercept the next day, and each time this proved correct. The raiders were practiced at sending out false messages which cancelled the distress calls of those ships they had captured.

On 10 September 1940, using this technique, the Benarty was secured and more secret mail seized, then, on 11th November, the Blue Funnel steamer Automedon (7.528 Tons) was intercepted by the Atlantis off the Nicobar Islands, in order to stop her using her radio to send a "raider sighted" report, the Atlantis shelled her with 28 rounds from her 5.9 inch guns (wrecking the vessel and killing Captain McEwen and two officers and a steward on the bridge).

The German boarding party was led by Lieutenant Ulrich Mohr, who had an excellent knowledge of English, forcing open the strong-room they seized some 60 packages of mail including all the top-secret post en route for Far Eastern Command, Singapore. Among their haul were the new Royal Navy fleet ciphers and the new Merchant Navy ciphers valid from 1 January 1941, also Admiralty weekly shipping intelligence summaries, and a host of other sensitive documents, there was also six million dollars of new Straits currency notes, fresh from the Treasury printers in England.

The single most important item packed in its own weighted canvas bag marked "SAFEHAND—BRITISH MASTER 0\Ls", was a copy of the War Cabinet Minutes for 8th August 1940, which included the highly secret Chiefs-of-Staff report on the defence of Singapore and the Far East against Japanese attack, which was being sentto Air Chief Marshal Sir Robert Brooke-Popham, C-in-C, Far East. This document consisted of 87 detailed paragraphs, and was most gloomy in tone. It flatly stated that Britain "was not" in aposition to resort to war if Japan attacked French Indo-China or Siam, and that Hong Kong, Malaya. Singapore, and the Dutch East Indies were indefensible since we would he unable to spare sufficient forces from other theatres of war to match the Japanese.

It seems incredible that such a valuable document should have been sent to the Far East on a slow, vulnerable, merchant ship when the flying-boat service to Singapore was still in operation.