"
A tiny mike, Tom explained, would be installed on the inside of each
face mask, with its output feeding to a sonar transducer on the
exterior. The receiving transducers would feed from amplifiers to
earphones. The hookup would be powered by the solar battery in the
hydrolung power unit, by connecting wires through the breathing tube.
"That's neat, Tom," Bud said. "Need any help?"
"You can mold us a pair of new face masks--big enough to cover the
earphones," Tom suggested. He handed Bud a penciled sketch from the
workbench, adding, "Then drill the holes for the mikes and
earphones--the dimensions are there on the drawing. But watch it so
you don't crack the plastic."
[Illustration: _Chow was wild-eyed with panic!_]
While Bud complied, Tom began assembling the tiny electronic parts. In
two hours the gear was ready for testing.
Tom wiped his perspiring forehead and gave Bud a grin of satisfaction.
"Go get your swim trunks, fly boy. Let's give it a tryout in the tank."
"Swell idea! Be back in a jiff!"
After a quick change, the boys strapped on the new hydrolung equipment.
Before adjusting his face mask, Tom mentioned that he had inserted
scrambling circuits into the communicators to foil any enemy
eavesdroppers.
"If they do pick up anything, it'll sound like chop suey," Tom ended
with a chuckle.
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