500.A15a3/644: Telegram

The Ambassador in Japan ( Castle ) to the Acting Secretary of State

11. Repeat to London.18

The only public explanations of the Japanese position with respect to cruisers are based upon formulae representing the strength of opposing sides in the great sea battles of the past, for example, the comparative strengths of the Japanese-Russian fleets in the battle of the Straits of Tsushima, or, of the British and German fleets at the battle of Jutland, and attempt to adduce from the figures the principle that a superior fleet could not be assured of victory unless it had a preponderant relative strength of 10–7, and, conversely, that fleet weaker than its enemy by any proportion less than 7–10 would be certain to meet defeat. It is the opinion of our own Naval Attaché as well as that of other Naval Attachés in Tokyo that this is rubbish.
[Paraphrase.] It is undoubtedly only in connection with war with the United States that the 10–7 ratio is considered. The Japanese naval experts believe that the United States in such an event would not permit the development of a war of exhaustion but as soon as possible would seek a final conclusion. This belief is based on the reason that the United States would have to bring over an effective military force; that the use of the best part of the American merchant marine would be required for the transportation of a large army across the Pacific; that the capture of American carrying trade by British and other foreign merchant marines and the loss of the United States foreign marketing would result from the diversion for a long period of time of a large proportion of American merchant vessels. It is consequently believed that as soon as possible the American Navy would try to come to grips with the Japanese Navy.
The great distance between Pearl Harbor and Japan, it is believed, would prevent the American battle fleet from effectively carrying on offensive operations against Japan from Pearl Harbor. The American battle fleet, therefore, would immediately upon the outbreak of war proceed to Manila in order that they might operate against Japan from that base which is close enough to permit the freest use of cruisers and submarines as well as of capital ships. The Caroline and Marshall Islands, through which the American battle fleet would have to pass, are mandates of Japan. Excellent places for concealment of submarines are afforded by these islands. For attacks upon the American battle fleet the Japanese would here undoubtedly exploit [Page 10] the use of the large submarine contingent upon which they insist. The Japanese realize only a portion of the battle fleet could be destroyed by their submarines, but they appear to have confidence in their ability to destroy enough ships to reduce the preponderance of the American battle fleet, thus making it possible for the Japanese fleet to meet the American fleet on terms which would be more or less equal.
There is naturally no public discussion of the above but undoubtedly the demand for a 10–7 ratio would largely disappear if Japan could be made to understand that we have no plans in regard to China which might conceivably lead to war. [End paraphrase.]
  1. Transmitted to the American delegation as Department’s telegram No. 19, January 25, 9 a.m.