The heart of the subchaser was its listening devices. It took skill to use these devices and achieve an accurate bearing. In the Tactics and Equipment section of this site you will find technical information about the listening devices. This is the informal story, told in the form of a couple of clips from The Subchaser Post, Vol. I No. 6, November 1920.
America Develops "Listening" - Excerpt from With the Channel Chasers, by Nathaniel Rubinkam
...The idea of listening for sounds under the water was not new when the United State entered the war. The Germans had used various kinds of hydrophones. The British navy was similarly equipped. It remained for American genius to develop the systems already employed and to add new secrets of the sea.
We learned to tell not only where a submarine was operating at a specific moment, but its exact distance from our own ship, and the direction in which it was moving. So delicate were the hearing devices and so well trained were the men who used them that it took but an instant to tell whether the sound of a ship's propeller was that of a submarine or a destroyer. Other sounds besides those of propellers were distinguishable under water - sounds within the submarine itself; the noise of its auxiliary machinery or even the weird scratching and tapping when repairs were being made inside its iron hull, and finally sounds that belong to the mysteries of the sea.
What are these sounds like? Not until you have listened and heard the numerous sounds within the sea's depths can you know. For there are many sounds besides that of the submarine. For instance, on Sept. 6, 1918, one of the units in our detachment operating in British waters, heard suspicious sounds which were reported by the listeners on both ships. The report showed that this sound came from a distance of 1,000 yards. A moment later a large whale came to the surface at the position indicated. The listeners continued their work and picked up further suspicious sounds. A chase was started and the ships followed the sounds for several hours. Deeming the ships in position to attack, depth bomb charges were discharged and the ships listened again to learn the result. Two large whales now came to the surface and remained there about fifteen minutes. Then the listeners again heard odd tapping sounds from two sources which had a regular beat - unlike any sound made by a submarine. These were the sounds that had been chased for more than three hours and it was probable that the listeners had picked up what were either heartbeats or respiratory sounds of the whales...
A Good Listener, by John C. Marden (excerpt)
Rookie Robertson, a real southern fellow both in appearance and speech, came aboard the 322 as a listener. He was a wonderful man on the tubes and never made a mistake.
While on drifting patrol off the coast of England one very calm day, Rookie happened to be on watch at the tubes. A few of us fellows and the captain planned a joke on Rookie to test his skills as a listener. We made fast a rope to a bucket and hung it overboard about four points aloft the port quarter. With a boat hook we kept hitting the bucket lightly until Rookie reported to the captain a peculiar sound bearing 250 degrees. Slowly we pulled the bucket along the port side until it was just opposite the tubes. He reported the sound coming closer and each report was correct in all respects.
In the meantime the radio man was delivering a false report to the captain in regard to another boat in our unit having seen a submarine submerge and head in our direction. Louder and louder we kept hitting the bucket and Rookie kept reporting it coming closer and closer. All at once we pulled the bucket out of the water and placed it on the starboard side and started hitting it the same way. Right away Rookie reported its new location and stated that it must have been a sub because it passed under the boat. Just as he made that report, someone called out: "Submarine sighted, broad on the starboard beam."
I think Rookie broke all records in coming up from the listening room. He was a "There's no use of my listening on the tubes for a submarine when you all are up here looking at it." He was rather disappointed when he found there was no submarine there, but nevertheless took the joke as only a real sub-chaser man could...