Captain Arthur J. Hepburn, Commander, Submarine Chaser Detachment Three, to Vice Admiral William S. Sims, Commander, United States Naval Forces Operating in European Waters
<No. 46L:1-L> 10 October, 1918.
From: Commander Subchaser Detachment Three.
To : Force Commander.
Via : Chief of Staff, Destroyer Flotillas.
SUBJECT: Listening devices – Efficiency of.
Reference: (a) Force Commander’s letter 0.4. 33410, of 9 September, 1918.
1. The following notes covering the experience of this detachment in connection with listening devices, are submitted in accordance with reference (a). These notes are altogether in connection with mechanical features of the apparatus. As regards the relative acoustical properties there is nothing to add to the information issued by the Special Board. The MB tube is a better instrument than the S.C. but harder to handle and more subject to injury.
(a) S.C. Tube. Very dependable and satisfactory. Only four receivers have been renewed on the 30 sets of this apparatus in the detachment.
(b) MB Tube. This apparatus is now generally in good condition. Considerable trouble was experienced at first through leaky receivers, and a general overhaul of all tubes has taken place. The principle improvement has been attained through removal of the cement used on the receivers and trueing up receiver seats. Only one tube that has been overhauled has required a second overhauling. It is too soon as yet to say that the troubles have been permanently overcome, but the condition is satisfactory at present. No vertical members of this tube have been bent. One horizontal member was bent. The tube sometimes sticks in raising and lowering, due generally to the use of poor quality of packing rather than being packed in improper manner. Satisfactory packing has been secured.
(c) Counterweights should be provided for both the S.C. and MB tubes. Request has been made for them.
(d) The collars used as distance pieces on the SC tubes should be split in order that they may be put on or taken off without disassembling the hull fitting. This is being done. There is an impression, not yet fully confirmed, that the use of the collar on the SC tube, bringing it so close to the keel, materially increases the water noises.
(e) K-tube. Generally satisfactory. A few rats have shown insensitivity. No spares on hand. One tube that became inoperative is accounted for by mechanical injury sustained when tube came adrift on deck. The principle defect in this apparatus is the time necessary to get it out and in. Much improvement can be made in this feature through proper drill. To expedite handling this tube over the side in taking in it is suggested that a short hauling line be attached to one corner of the triangle with the other end stopped to the cable at a distance of about 20 ft. This would allow the triangle to be hauled up in a vertical position with less risk of injury.
2. With regard to the failure to execute a successful attack after sound contact has been gained this detachment has had no experience in actual operations upon which to base any conclusions. Considerable thought has been given to the subject and it is believed that the following considerations are pertinent.
(f) Comment by chaser personnel on this subject is insistent upon making the attack at the earliest possible moment after sound contact is gained. Undoubtedly it is a point of major importance. It is worth considering, however, whether this feeling is not prompted principally by the fear of losing sound contact and not bringing off any attack at all, rather than by a careful analysis of all the factors in the problem. It is good doctrine but it is believed to be questionable thumb rule to apply to all cases.
(g) The depth charge allowance of chasers is somewhat limited. With proper ship handling, three chasers acting in concert can lay a more concentrated pattern than any other type of craft. These two facts point strongly to the old gunnery principle that there is no surer way to miss than by shooting an improperly aimed or improperly ranged shot. If the depth charge allowance were large enough more of a compromise could be made on the line of barrage-fire.
(h) In an attack from a point 400 yards distant from a submarine making 7 knots, three chasers at a speed of 14 knots can barely lay a pattern that will make a reasonably sure hit, and then only upon the assumption of a known course of submarine at the time the attack is begun. Such an assumption is unsound. It appears that a six boat attack should be developed since there may be frequent occasions when two units will be able to attack in concert.
(i) The above are theoretical points. It is believed that they may all be settled by the following procedure which is being put into practice at this base. In the first place it must be realized that the accurate laying of a predetermined depth charge pattern by three boats acting in concert is not an evolution which can be performed with skill and certainty from a mere paper knowledge of the principles. Actual attacks during operations will be rare, and it is essential that the chasers act with the utmost possible precision and promptness upon these occasions. The necessary skill can only be acquired and maintained through constant practice. It has, therefore, been ordered at this base that the Squadron Commanders will exercise each unit coming off patrol in at least one attack during its “in port” period. It is possible to carry out these maneuvers inside the harbor and in connection with movements for fuel, water, etc. Vari-colored buoys to represent depth charges, - mere blocks of wood that can be thrown for fifty yards, are used. Pistol shots or whiltle [i.e., whistle] will represent depth charge explosions. An anchored mark, such as a mooring buoy,is used to represent the fix obtained on a submarine, and when a motor dory can be obtained it will be used for a sound-maker and moving mark. For the present only the one form of straightaway attack by three boats in line is to be concentrated upon until the personnel become skillful in its execution under various conditions of vessels headings, etc. It is believed that this practice will lead to much valuable information on the subject and the development of a better form of attack.