Captain Richard H. Leigh, Operations Section, Anti-Submarine Division, United States Naval Forces Operating in European Waters, to Planning Section, United States Naval Forces Operating in European Waters
U.S.NAVAL FORCES OPERATING in EUROPEAN WATERS
22nd August 1918.
Memorandum: For Planning Section.
Subject : Effect of Sound Detection Development on Scouting.
1. The interest and energy which the destroyer flotillas have shown in making application of the recent developments of sound detection apparatus, together with the continual development taking place in the instruments themselves will soon make possible a new method of scouting, more direct, certain and expeditious than has hitherto been possible. For in scouting by sight alone there occurs periods of low visibility or extreme darkness, durinh which the scout line must retire at enemy’s speed of advance, or take very serious chances of missing the contact by passing the enemy during darkness.
2. These retirements increase greatly the time required to scout a given area, they are a big drain on the fuel consumption and corresponding sea-keeping ability of the scout, and as periods of low visibility-except normal night-cannot be predicted, they are liable to upset most careful plans of operations.
3. When the development of sound detection apparatus has reached such a point that it may be relied upon to hear the vessel scouted for a distance greater than one half the distance between scouts, the scout line will no longer have to retire during low visibility or darkness, but may continue its advance with suitable listening periods depending on the dependable range of the instruments and the relative speed of approach of the scouts to enemy. This will greatly simplify the problem of scouting, just as the invention of radio did in permitting greater distance between scouts, and in reducing the numbers of relaying vessels necessary to report the contact. It will be of further benefit to torpedo vessels, as it will enable them to make contact and assemble, during low visibility when there is the greater chance of successful torpedo attack.
4. The present devices for the detection of submarine by sound are chiefly deficient in, either their inability to detect at a satisfactory distance faint noises as of a submarine at slow speed, or if sensitive enough to do this, they are objectionably sensitive to interferring noise of passing traffic. This presents in use of detection devices for detectingsubmarines, certain difficulties which are not unusually encountered in scouting where the opposing ships are generally large and often numerous and the search is conducted in waters free from passing traffic.
5. Particularly is this the case in the present use of scouting to make contact with either large valuable ships justifying an escort, or with a convoy of ships. In both of these cases the vessels sought are excellent noise makers, and already there are noise devices available which will hear them further than the eye can see. In addition the contact must be made well out at sea beyond the area of conjested traffic: so that the very best conditions prevail for sound detection.
6. Our hunting vessels equipped with drifting “K” tube are having constant practical experience at hearing vessels below the horizon, indeed their great complaint is that they hear too far thus making in too many interferring noises. there is no question of the ability of this device, when used by trained listeners, and with all ships noises reduced to zero, to hear large ships, and especially high powered ships and convoys below the horizon.
7. Therefore, it is believed that when the destroyer personnel have learned the use of this instrument it will be of great value to them in meeting convoys. There normally occurs about the time when contact is due and the visibility, as so often is the cases in these waters, is low, a period of uncertainty when the scout commander hesitates between running back and pressing on. Particularly is this the case in meeting ships where speed is 20 knots or more, when a run by of 30 minutes, may mean a stern chase at high speed for five or six hours. A practised personnel could insure prompt contact without risk of being passed by the use of sound detection.
8. The use of this method in thick weather is not recommended with the personnel in its present untrained state. But, it is suggested that when a scout line has made sight contact in good visibility, and it is convenient to do so, that the vessels on prearranged signal stop and make use of their K-Tubes to listen. In this way the possibilities of the method will be demonstrated and the destroyers’ commanders can judge for themselves the advisability of xxxxxx using it in thick weather. The personnel will obtain practice, and the time spent will not be wasted, as, if a satisfactory method is developed it will be of great value during the short days and poor visability of the winter.
9. The familiarity thus obtained with the use of the sound detection for the simple problem of detecting large noisex making vessels, will be a valuable training, leading to the more difficult problem of submarine detection submerged.
R. H. LEIGH