"That's right," Steve agreed. "Anyway, there were several different stations, in different locations. Some were on islands, some on fishing boats. Since they operated only in short bursts in a random pattern, the subs—and the special teams we sent out—were never able to get a bearing that meant much."
"They must be self-recording," Rick said thoughtfully, "otherwise the enemy couldn't get the information out of them."
"They are. Whatever echo they get makes a tracing inside the box they're mounted on."
Scotty objected, "But what kind of information is it? How can anyone tell anything about the subs from such recordings?"
"By putting all the recordings together and running a rather complex analysis. The analysis will give speed, depth of operation, maneuverability—if the spies are lucky to have beams operating at the right time—and number of torpedoes fired, with the same information on the torps. That's enough information to make it worth an enemy's while."
"I'll say!" Scotty turned to Zircon. "And what were you doing, Professor?"
"I'm afraid I arrived on the scene too late to do much good," Zircon boomed. "However, I believe we can be useful in preventing such occurrences in the future. I have an idea for an improvement in our scanners that will allow a fix to be made on such beams."
There was a pause when dessert arrived. The boys savored excellent apple pie smothered in a generous helping of ship-made ice cream.
"We thought Zircon might help us work out a system of getting fixes on the transmitters," Steve said. "As it happened, we got a lucky break. The subs happened to have their devices pointed at St. Croix simultaneously when a beam scanned them. They got a fix on it. We flew a team of frogmen down in a Navy amphibian right in the middle of the second storm. They found it, and got the men who were handling it. One of them talked."
Jimmy Kelly picked up the story, "You arrived with Zircon at about the same time the St. Croix team took off from our base, and headed right into the storm. They didn't get back until late last night, and it was nearly dawn before we got the story from the man who talked. Then we loaded on this DE and headed here."