or the
forgotten beach party.

"But let's not wait too long for the next date," Sandy warned playfully.

"Okay, that's a deal," Bud promised.

The next morning at the plant Tom called on Harlan Ames. He told of the
sinister hoax by the caller who had passed himself off as Lester Morris.
The security chief promised to investigate.

"I'll tip off the police about Len Unger," Ames added. "If they can find
him, we may be able to crack this case wide open."

Tom telephoned Bud, Hank Sterling, and Arv Hanson to meet him at the
helijet hangar. The four took off in one of the Swifts' Whirling Ducks,
which was standing by loaded and ready. Soon they landed on Fearing
Island, where Tom would try out his antidetection invention.

"What'll we use for a test sub, skipper?" Hank asked as they drove
toward the docks.

"A jetmarine," Tom replied.

A truck with engineers and technicians was following the jeep. It
carried the equipment which Tom and Bud had assembled the previous day.

When they arrived at the docks, Tom gathered the men in a loading shed.
He showed them his drawings and explained how his "sonar-blinding" setup
would operate.

"Don't let the diagrams fool you. The basic idea is very simple. We
absorb all sonar impulses that hit the ship and transmit them out the
opposite side of the hull, instead of letting a ping bounce back and
show up on the sonarscope of any hostile sub on the lookout for us."

Most of the job, he went on, would be tedious detail work. It would
consist of attaching hundreds of mikes and speakers all over the hull to
pick up and transmit the sonar pulses. The mikes would be receiving
transducers and the speakers would be transmitting transducers.

"The leads from them," Tom ended, "will be centralized in a single
electronic control unit inside the ship. I'll handle that part of it."

"Great idea, Tom!" Arv Hanson said admiringly.

"But what a job it'll be rigging those transducers," put in one of the
technicians.

Tom nodded wryly. "You're right, Danny. If this experiment works out,
though, I think I can lick that problem on future installations."

The young inventor explained that he hoped to find a way to mold the
transducers into a continuous plastic sheet. This could be applied to
the hull of a submarine in a single operation.

"But this time we'll have to do it the hard way," Tom added with an
apologetic grin.

A jetmarine was hoisted into drydock and the work crew swarmed o