"You may have a tough time finding gardeners, Dad," Tom pointed out. "Men can't work that far down for very long at one time." "It'll be a problem," Mr. Swift conceded. He finished his coffee, then looked up with a twinkle in his eyes. "How about figuring out a solution for me, Tom?" "A new kind of air lung?" Tom was intrigued! CHAPTER IV AERIAL ATTACK "Yes, son," Mr. Swift went on. "What's needed is a new type of breathing device--one that will eliminate bulky air tanks and permit a skin diver to stay down for long periods." "Quite an order, Dad." Grabbing a pencil, the young inventor began sketching. In both his Fat Man suits and his osmotic air conditioner, Tom had already perfected ways of drawing oxygen from sea water. "But a small gadget for skin divers," he said, "will take a fantastic job of electronic miniaturization." After a pause he added, "It could really speed up recovery of the Jupiter prober, though." Lunch over, Tom hopped a jet scooter and sped off to his private laboratory. The modernistic glass-walled structure--designed by Tom himself--had every tool of modern scientific research, from electronic microscope to helium cryostat. As always, whenever he was absorbed in a new idea, Tom was eager to get to work. "Let's see what I'm shooting for. A small container, slung around the diver's neck?... No, too dangerous. Better hook it to his weight belt, with a tube to his face mask." Using a plastic foam "breadboard," Tom began experimenting with various circuit designs. He worked through the afternoon and returned to the problem early the next morning. He was interrupted by a message from Art Wiltessa, reporting no luck so far in finding the missile. Later, shortly before lunch, Tom received another 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.