"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.