The sonar operator (聴音兵 Chōon-hei) was an unnamed Kriegsmarine sonar operator and crew member of the U-234.

He was a German man with a skinny build, pale skin, short blond hair, and a mustache and beard. He wore radio headphones and a dark green uniform.

When the U-234 was near the Nicobar Islands on March 25, 1945, the sonar operator was checking the area for Allied ships. As the U-boat traveled stealthily beneath the ocean surface, he noted that one enemy ship had just passed over them. Captain Wentzel H. Ahbe then ordered Fritz and the others to make two turns in their course. Continuing to monitor the area, the sonar operated stated that he was detecting sound from another vessel in front of them. To his surprise, he immediately detected another signal, realizing that their enemy was coming out in numbers. Changing the course again, Ahbe ordered his men to put both engines at full power and fire a torpedo. In response, one U.S. Navy ship moved away, so Ahbe had the U-234 cut her engines in order to travel silently. At that point, another American ship traveled above them, with the sonar operator warning his crew mates that the enemy ship was using active sonar. A few seconds later, the American ship deployed a few depth charges that hit the U-boat, causing it to sink to a depth of fifty-seven meters. The men in the forward torpedo room advised Ahbe to close off the fore hatch, which he did.

In the operations room, the sonar operator listened to Ahbe conclude that they would die because their engine and ballast were damaged beyond repair, and they would lose oxygen in the next two hours. Being relieved of his military duties by his captain, he and other sailors mourned together before they died.