also installed
the analyzer sonar in the _Sea Hound_.

"Want to be 'It' for another underwater game of hide-and-seek?" Tom
asked Bud with a grin.

"Sure, but don't tag me with a torpedo!"

Minutes later, the jetmarine slipped off into the depths with Bud and
two other crewmen aboard. Tom and Arv followed in the seacopter. The
quality analyzer sonar worked even better than Tom had hoped. He not
only tracked the jetmarine on its outward course, but located it three
different times after shutting off the analyzer long enough for Bud to
seek a new location.

"How'd you like to relieve Hank in the South Atlantic?" Tom asked Bud
upon their return.

Bud gave a whoop of excitement. "Roger!"

Tom slapped him on the back. "You can take off as soon as your ship's
provisioned. I'll join you later--but first," Tom added mysteriously, "I
have another job to attend to."

CHAPTER XVII

A MISSING AMULET

Bud's curiosity was instantly aroused. "Don't tell me you have a new
trick up your nautical sleeve to fox the Brungarians?"

Tom grinned. "That's the general idea. I hope to give hydrolung divers
the same protection that your jetmarine has."

"You mean make them invisible to sonar?"

"Yes," Tom replied, "and also give them personal spy gear to probe the
waters around them and spot an 'undetectable' enemy."

Bud whistled. "Do that, and I'll say you're _really_ a magician,
skipper!"

Tom himself transferred the analyzer from the _Sea Hound_ to Bud's
jetmarine. On a chance that it might become necessary to operate at
greater depths--either in searching for the lost missile or in shadowing
the enemy--Tom also assigned Arv Hanson the job of rigging the _Sea
Hound_ and another seacopter with his new inventions.

Four crewmen volunteered for the cruise. When the jetmarine was ready,
Tom and Bud exchanged tight handshakes.

"Good luck!"

"Thanks, Tom."

The young inventor waved as Bud disappeared down the hatch. As soon as
the craft had submerged, Tom went back to Shopton. That evening the
Swifts were enjoying a quiet dinner at home when a loud, growling buzz
shattered their mealtime conversation.

"Oh!" Sandy gasped. "The burglar alarm!"

The Swifts' house and grounds were protected by a secret magnetic field.
Any intruder breaking the barrier touched off the automatic alarm
system. To avoid the buzzing, the family and their close friends wore
wrist watches containing tiny neutralizer coils.

"I'll see who