British naval officers conducted a daring spying mission on Japanese-controlled islands in 1933 while sailing around the world, newly discovered papers have revealed.

Five officers claimed that they were making an amateur attempt to circumnavigate the globe. They were, however, secretly assessing the Kurile Islands as a prospective military base.

Eight years later the Japanese armed forces used the islands to hide six aircraft carriers that destroyed the American fleet in Pearl Harbor.

The papers, which read like an extract from Erskine Childers’s pre-First World War spy thriller The Riddle of the Sands, have emerged from the estate of the late Commander Robert Ryder, VC, the sailing master of the officers’ yacht.

Historians believe they show that the British had guessed Japan’s hostile intentions and seen the great military potential of the islands much earlier than thought previously.

Nick Hewitt, the naval historian for the Imperial War Museum, said: “This is a remarkable find because it is clear proof that the Royal Navy was thinking of a possible war with Japan as early as 1933. It comes straight out of the Boy’s Own Paper – these young officers put forward their own plan and were adventurous and daring enough to take on the Japanese.”

Until now it was always thought that the five – Lieutenant Ryder, Lieutenant George Salt, Lieutenant Philip Francis, Lieutenant-Commander Martyn Sherwood and Surgeon-Lieutenant Carew Ommanny-Davis – had engaged in an adventurous voyage to see if they could sail across the world “the wrong way round”.

As civilians they commissioned and built the ketch Tai Mo Shan to sail home to England from Hong Kong against the prevailing winds through Japan, the Bering Sea, Panama and the West Indies.

But Ryder’s personal documents reveal that the crew proposed to Naval Intelligence that they would examine the military potential of the Kuriles, a volcanic island archipelago stretching 700 miles northeast from Japan. The islands were sparsely populated, shrouded in fog six days in every seven and were believed to have deep ports required for warships and submarines.

On his planning notes for the voyage, Ryder stated that the first aim was to find possible bases for British vessels close to the Japanese islands: “1. Intelligence Report on all places visited . . . Observing any possibilities advanced base for submarine operations, or as a W/T [wireless transmitter] or W/T F. [wireless interception] in the event of hostilities against Japan or between Japan and America.”

Before sailing, the crew asked the Japanese authorities for permission to sail close to the islands, but the Japanese Foreign Minister refused.

In July 1933 the crew berthed at the port of Nemuro on the tip of Hokkaido, only 50 miles (80km) from the islands. In a report sent to the Director of Naval Intelligence in London, the crew wrote that their route had attracted the close attention of Japanese naval officers.

“We were subjected to close cross-examination through an interpreter, by someone we suspected of being a naval authority,” the report reads.

“From the interrogation it was obvious that the Japanese had something of a secret nature in the Northern Kuriles. Pointing to the island of Paramushir [one of the islands] they wanted to know how far off it we would pass and what day! What was our daily progress? And could they verify this from the log?”

The report says that after sailing into Japanese waters the crew were forced by the Imperial Navy to abandon their plans for a night-time landing on the islands. “The possibility of paying Paramushir a nocturnal visit was under consideration . . . but it was so obvious that [a Japanese naval ship] would be waiting for us that the project was abandoned,” it reads.

The military significance of the islands emerged after the raid on Pearl Harbor. On November 22, 1941, the Imperial Japanese Navy gathered at the islands, where they could hide from American spotter planes.

The Riddle of the Sands, first published in 1903, told the story of a yachting expedition that uncovered German intentions to wage war on Britain. Winston Churchill credited it as a reason for the Admiralty establishing naval bases at Invergordon, the Firth of Forth and Scapa Flow.

During the Second World War all five crew of theTai Mo Shan fought in the front line. Ryder won the Victoria Cross in 1942 for commanding naval forces in the raid on St Nazaire. He died in 1986, but his papers have been disclosed by his son, Canon Lisle Ryder, of Pyworthy, Devon.

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