Naval History and Heritage Command

Naval History and Heritage Command

Descriptive Specifications of “C” Tube Set





November 22, 1917.




     The so called “C Tube Sets” are devices by means of which the noises made in water by vessels whether on the surface or submerged can be heard and the direction of their source with reference to a listener ascertained with a great degree of accuracy. This device is operated only by compressional waves in water and these water waves are transformed into air waves which[h] are made to impinge upon the ears of the listener.

     “C Tubes” are not electrical but wholly acoustical.

     The C tube sets make use of the principle that, with the normal separation between the ears of a listener, he is able to ascertain the direction of a source of sound in air by the unconscious effort of noting the differences in the times of arrival of the sounds heard in his two ears, if one ear is nearer the source of the sound than the other. By turning his head until the times of the arrival of the sounds in both ears are the same, the listener will be facing directly toward the source of sound.

     If the ears of the listener could be held under water, it would be possible to hear sounds and determine the direction of the source in precisely the same manner, were it not for the fact that the velocity of sound waves of the same pitch is greater in water than in air. As a consequence, if the direction of a source of sound in water is to be ascertained in the same manner as it is in air, the separation between the “water-ears” must be proportionally increased.

     The “C” Tubes are rubber pipes or bulbs closed at one end and are the “water-ears”. These tubes are at the end of a cross-arm between five and six feet long, thus giving the necessary separation between the “water-ears” to make it possible to note the differences in the times of the arrivals of the sound waves. The other end of each “C” tube is connected by a small tube with the human ears of the listener. The “C” tube and cross-arm can be turned by the listener by means of a hand-wheel and “T” pipe – which gives the required submergence – until the sound seems directly ahead of him in precisely the same manner that the head is turned in listening to air sounds. A scale near the listener shows the position of the cross-arm and consequently indicates the direction of the source of sound when the observer has turned it until the source of the sound seems directly in front of him.

     “C” tube sets are designed to be swung overboard from the side of a vessel when they are required for use. The general arrangement of this apparatus when in service is illustrated in Figure 1.1 A more detailed illustration of the “C” tube set is shown in Figure 2.2

     Devices.  The form of “C” tube set now manufactured is that shown in Figure 2, and is furnished with three lengths of “T” pipe. The characteristics of these three forms are as follows:

Form 16, length of “T” pipe, 15 feet. Length crossarm 5’8”

    16,                 20                    5’8”

    16,                 25                    5’8”

     The weights of complete equipment are as follows:

Form 16.


Weight “T” pipe, gimbal ring & hand-wheel.

Weight out-rigger & Pipe seat support

Total Weight

15’ “T” pipe













     The following spare parts are furnished with each set:

Two (2) C Tubes.

Two (2) Trunnion bolts

One (1) Pair terminals with tubing

One (1) Pair terminal tubes

Six (6) Terminal tips.

Two (2) Celluloid bearing calculators.

(a) 4-90 degree scale and 360 degree scale

(b) Both scales 360 degrees

     These spare parts are illustrated in Figure 3.

     Information Necessary with Orders. The Submarine Signal Company is prepared to furnish the “C” tube sets described above, and with each set the above specified parts. In ordering this apparatus it will be necessary to designate the number of “C” tube sets, Form 16, required, as well as the lengths of “T” pipes required.

Source Note: TD, DNA, RG 45, Entry 520, Box 338. Document reference: “S-12.”

Footnote 1: See: C-Tube Illustration #1.

Footnote 2: See: C-Tube Illustration #2.