Last month we looked at the reel and compensator for the K Tube hydrophone used on U.S. submarine chasers in WWI. This time, a look at the K Tube frame.
The K Tube wasn't really a "tube" at all, in the sense of the C Tube and other types of hydrophones. It was a triangular frame with a microphone ("rat") cased in rubber at each corner. Each of the microphones was wired through the main cable to the receiving apparatus (the compensator).
To listen for submarines, the crew would throw the frame overboard and allow it to drift away from the boat. A main float held the frame a fixed distance under water, and floats along the cable allowed the crew to see the bearing of the frame relative to the boat. A Listener would select a specific pair of microphones. The sound from one would be directed to one ear and the sound from the other to the other ear. The compensator allowed the Listener to adjust the volume of one relative to the other. When the sound was the same in both ears, the bearing of ths sound source relative to the frame's bearing could be computed based on how much the compensator dial had been rotated. Switching to another pair allowed the Listener to get a second, confirming reading.
In early tests performed out of the Submarine Signal Company station at Nahant it was determined that "For any sea in which the boat can be used for chasing, K-Tubes are free from water noise and its range as indicated by the tests is upward of 20 miles for surface craft, 12 miles or less engine rhythms come in distinctly. At greater distances, the pulsating character disappears and the only sound received is a high pitched continuous roar upon which direction can be obtained, but character not determined until the ship comes nearer."
In some attack reports, like the SC 93 attack report described in my book (Hunters of the Steel Sharks, the Submarine Chasers of WWI, prologue), the K Tube seems to be used as an initial listening tool, to see if any sounds worth pursuing can be heard. It would have been harder to deploy and use than the C Tube hydrophone, for example, so possibly not the first choice when stopping to listen during a chase. But it stands out one of two electronic detection devices, the other being the Trailing Wire. We'll look at that next time.
Happy July 4!
—Todd Woofenden, editor