Part 17 (2/2)

”Natch! With a brain like yours, it's a cinch,” Bud quipped. ”Explain, professor.”

”Well, we can never do away with the noise of a sub's propulsion machinery,” Tom began. ”That goes without saying. So we'll have to camouflage it--lose it in the underwater jungle noises, so to speak.”

Bud scratched his head. ”How do we do that?”

”By amplifying the natural undersea sounds all about it,” Tom explained.

”Fish and all forms of underwater life make a background noise over the hydrophones, you know.”

As Bud nodded, Tom went on, ”So we simply step up the volume till the sub's own noise gets drowned out or 'wasted' in all the racket.”

This could be done, he concluded, with fairly simple amplifying equipment. Bud, Hank, and Arv were jubilant at the idea.

”Nice going,” Bud said. ”How soon can we give it a try?”

”Soon as I can rig up the amplifier,” Tom promised.

In less than two hours they were ready to submerge again. Zimby c.o.x joined the crew. Bud suggested taking along hydrolungs in case of any need for tinkering with the transducers or amplifying equipment.

This time, the jetmarine scored perfectly on the test, successfully eluding all the _Sea Hound_'s efforts to detect it. Tom returned happily to base, feeling that the antidetection problem was now solved. The jetmarine, however, failed to appear.

”That's funny. The test was over at four-fifteen,” Tom murmured.

”Maybe Bud surfaced out at sea somewhere,” Arv Hanson suggested.

Repeated radio calls brought no response. Tom, now seriously worried, took the seacopter down again for another search, hoping that Bud would have switched off the antidetection gear by this time. But neither sonarscope nor listening devices revealed the slightest clue.

Tom, Hank, and Arv exchanged fearful glances. Had the jetmarine foundered on the ocean bottom--perhaps fouled somehow by Tom's new invention? Or had Bud and his crew fallen victim to the enemy?

CHAPTER XIII

ENEMY FROGMEN

At the end of the test period, Bud had prepared to bring the jetmarine to the surface. But just as he was about to blow the ballast tanks, Mel Flagler sang out a warning from the sonarscope.

”Whoa! Hold it, skipper! I think we have company on the starboard beam!”

Bud jerked his head around in surprise. ”You mean the _Sea Hound_?”

”No, she surfaced,” Mel reported. ”Can't make this out yet, but it could be another sub.”

Bud turned the controls over to Zimby c.o.x. Then he rushed to the scope and examined the blip. ”Seems to be moving away from us on a westerly course. It's about two miles from here.”

He donned the hydrophone ea.r.s.et and listened. ”It's no seacopter, nor a jetmarine either,” he announced presently.

”A Navy sub, maybe?” suggested Zimby.

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