er call, this time from Admiral Walter. "Just wanted to keep you
posted, Tom. Our task force reports no success on their part in finding
the buried missile. No sign of the enemy, either."

"They'd probably hesitate to attack any official U.S. Navy units," Tom
said. "Or it might mean they've already found the missile themselves."

"That's what I fear," Admiral Walter confessed gloomily. "However, we'll
continue searching."

Tom promised to fly down to the site at the first opportunity, saying he
was developing a new device that might assist in the search. After
snatching a hasty lunch, Tom returned to work.

Arv Hanson machined several parts and molded the plastic face mask to
Tom's specifications. By evening the new device was completed.

"Now for a test," the young inventor said to himself.

Sandy Swift and Phyl Newton were eager to watch the test, so the next
morning they drove to the plant in Phyl's white convertible. Tom, clad
in swim trunks, was waiting for them with Chow near the edge of a
mammoth concrete tank. Set in bedrock, at one end of the Enterprises
grounds, the tank was used for submarine testing.

When Sandy saw the power unit strapped to Tom's weight belt, she
exclaimed, "_That_ little gadget will supply all the air you need? Why,
it's no bigger than a pocket transistor radio!"

Tom grinned. "I hope it will. That's what I intend to find out."

"How does it work?" Phyl asked, fascinated.

Tom explained, "Actually its function is to replace the carbon dioxide
that I exhale with fresh oxygen drawn from the water. Otherwise,
although the carbon dioxide I'd breathe out would be a very small amount
at a time, it soon would make the air unfit. The nitrogen, which makes
up much of the air we breathe, is chemically inert and can be used again
and again."

He pointed to a round screen on one side of the unit. "This is the water
intake," Tom went on, "and this other screen is where the water comes
out after we've removed its oxygen."

Near the forward end of the unit, a semirigid plastic tube was
connected, leading up to the face mask. At the rear was a power port for
inserting a small solar battery.

"What about this little tuning knob?" Sandy asked.

"That's the rate control for adjusting the output frequency to the
wearer's breathing rate." Tom added, "I've decided to call the whole
apparatus an 'electronic hydrolung.'"

Chow pushed back his ten-gallon hat and scratched his head dubiously.
"Wa