B.) YOU’RE THE CAPTAIN of an American destroyer escort. Your ship is equipped with sonar. You transmit a ping, wait for the echo, ping and wait for the echo. Though whenever you ping a U-boat, by the time its echo is received, by the time its echo is processed, the U-boat’s in another place, but then you’re in another place as well, nearer, or farther, because the U-boat’s also pinging you, and you echo, you can’t help it. All sonar can detect is the past. The future floats between predictions. The U-boat might maneuver you astray, in a countermeasure obscuring the angles of your search, and so keeping concealed the second boat that would sink you. Though you might sink the first boat first.