ObStrm Radermacher was portrayed as "Navigator Kirschbaum" in Das Boot. It was not unusual for Chief Petty Officer mechanicker mates to be promoted to Engineering officers, and not unusual for ObStrm (who would also be classified as "Chiefs" in American and British ratings) to be commissioned as commanding officers. In fact, leaving an ObStrm rank, going to Officer's school, serving as a junior watch officer, and then being promoted to command of a U-boat (as Radermacher did) is pretty much the standard track in such instances.