[derstosstrupp]

The reason for the use of the motors in port is because the diesels (to the extent they were even reversible, see below), were relatively more difficult and time consuming to reverse. You had to shut the engine off, shift the cams over and then restart it. As a weight-saving measure about mid war, reversible diesels were no longer supplied.

The motors on the other hand are very easy to reverse and quick. You simply place the speed rheostat on full field, switch the travel direction switch to the opposite direction, and you are done. This causes a significant initial surge in armature current, but the starting resistors can handle that until CEMF starts building in the opposite direction.