NAVY DEPARTMENT, OFFICE OF THE CHIEF OF NAVAL OPERATIONS, Washington, June 13, 1941, Op-30C1-AJ (SC)N20-12 Serial 055730 Confidential From: The Chief of Naval Operations To: The Commandant, First Naval District. The Commandant, Third Naval District. The Commandant, Fourth Naval District. The Commandant, Fifth Naval District. The Commandant, Sixth Naval District. The Commandant, Seventh Naval District. The Commandant, Eighth Naval District. The Commandant, Ninth Naval District. The Commandant, Tenth Naval District. The Commandant, Eleventh Naval District. The Commandant, Twelfth Naval District. The Commandant, Thirteenth Naval District. The Commandant, Fourteenth Naval District. The Commandant, Fifteenth Naval District. The Commandant, Sixteenth Naval District. Subject: Anti-torpedo baffles for protection against torpedo plane attacks. Reference: (a) CNO conf. ltr. Op-30C1 Serial 010230 of Feb. 17, 1941.
1. In reference (a) the Commandants were requested to consider the employment of and to make recommendations concerning anti-torpedo baffles especially for the protection of large and valuable units of the fleet in their respective harbors and especially at the major fleet bases. In paragraph 3 were itemized certain limitations to consider in the use of A/T baffles among which the following was stated:
"A minimum depth of water of 76 feet may be assumed necessary to successfully drop torpedoes from planes. About two hundred yards of torpedo run is necessary before the exploding device is armed, but this may be altered."
2. Recent developments have shown that United States and British torpedoes way be dropped from planes at heights of as much as three hundred feet, and in some cases make initial dives of considerably less than 75 feet, and make excellent runs. Hence, it may be stated that it can not be assumed that any capital ship or other valuable vessel is safe when at anchor from this type of attack if surrounded by water at a sufficient distance to permit an attack to be developed and a sufficient run to arm the torpedo.
3. While no minimum depth of water in which naval vessels may be anchored can arbitrarily be assumed as providing safety from torpedo plane attack, it may be assumed that depth of water will be one of the factors considered by any attacking force, and an attack launched in relatively deep water (10 fathoms or more) is much more likely.
4. As a matter of information the torpedoes launched by the British at Taranto were, in general, in thirteen to fifteen fathoms of water, although several torpedoes may have been launched in eleven or twelve fathoms.
R. E. INGERSOLL.Copy to CinCpac. CinClant. CinCaf. C. O. Naval Net Depot, Tiburon. C. O. Naval Net Depot, Newport. Comdt. NavSta, Guantanamo. Comdt. NavSta, Samoa. Buord. Op-12.