"They’ve seen us," Bischoff says. "We’ll dive in just a moment." But before he loses his ability to use the periscope, he does one more three-sixty, just to verify that his mental map of the convoy is accurate. It is, more or less; why, there’s a destroyer, right there where he thought it was. He steadies the ’scope, calls out target bearings. The Torpedomaat echoes the digits while dialing them into the targeting computer: the very latest fully analog technology. The computer grinds through some calculations and sets the gyroscopes on a couple of torpedoes. Bischoff says: fire, fire, dive . It happens, almost that fast. The diesels’ anvil chorus, which has been subtly driving them all insane for a couple of days, is replaced by a startling silence. They are running on batteries now.