“If only we’d arranged to send regular radio reports,” Bud said gloomily.
“Then Enterprises would be worried about our silence and start a search.”
“That was part of the risk we took. To send radio messages, we’d have had to surface at regular intervals, which would have devalued our underwater survival experi-” Tom broke off suddenly. “Bud! You’ve just given me an idea!”
“Great-let’s hear it. We can sure use one.”
“Enterprises is expecting to hear signals from us,” Tom declared. “At least Fearing Island is.”
“Signals? You mean-”
“I mean our sound-channel testing by SO-FAR-Sound Fixing and Ranging.”
“I don’t get you,” Bud said, puzzled. “You’re talking about those underwater detonations. But they won’t tell the hydrophone monitors back at the base anything about our safety. You brought the detonators to test for sound channels.
If signals are picked up, the island will just assume that we’ve encountered channels along our course.”
“I’m hoping the signals will be picked up, and that we can use the detonators for an SOS.”
Bud kindled with excitement. “Genius boy, that brain of yours is twenty-four carat! Let’s give it a try!”
The young inventor had brought a dozen of the small underwater detonators, set to explode at a
SOSI 15
four-thousand-foot depth. Tom had planned to drop them at wide intervals during the trip tť check the location of underwater sound channels, which carry noises for thousands of miles.
Instead, he now dropped three detonators in quick succession-then three slowly-then three more in fast succession. If picked up on hydrophones, the sounds would form a crude SOS in Morse Code-dit-dit-dit, dah-dah-dah, dit-dit-dit.