"It's a sub, all right," he said a short time later, listening again over the hydrophones.
"Pretty close to Fearing Island, isn't it?" put in Mel Flagler. "That's a government-restricted area."
Bud nodded grimly. "But staying just out of sonar range from the base."
The jetmarine closed steadily on its quarry. In a few minutes they were able to make it out dimly through the cabin window, dead ahead.
"That's sure no U.S. Navy sub that I know of," Bud said. "Probably an enemy snooper."
"What if they spot us?" Zimby asked.
Bud chuckled. "That's the beauty of it, pal! Don't forget. With this new antidetection gear we're invisible to them. At least as long as they don't run into us or we into them," he added.
"Or unless they have superdetection equipment we don't know about," cautioned Mel Flagler.
As they talked, the unidentified submarine was bearing steadily toward the mainland. Fathometer soundings showed it was on a steep upward slope of the continental shelf.
Presently a foaming gush of bubbles showed that the sub ahead was blowing its tanks. The jetmarine followed as it surfaced and Bud hastily manned the periscope.