Sonar Knowledge

"It would have to," Marco interjected. "Too many subs out there in the deep, blue sea. There are still sensors all over the ocean floor from the Cold War."

<Exactly,> Ax agreed.

"Echolocation?" Cassie suggested.

"Echolocation is a lot like what they call 'active sonar,'" Marco said. "You bounce sound waves off an object and listen to the echoes. But subs don't use active sonar, usually, because if you're 'pinging' someone with active sonar, they can hear you. Subs usually stick with passive listening."

"Marco, are you just pulling all this out of the air? How do you know all this?" Rachel demanded.

"Tom Clancy."

I nodded. "Tom Clancy. The Hunt for Red October."

"You should read something besides Glamour, Rachel."