I understand that it's tough out there at night,what with all those waves and darkened ships sliding through the sea. Submarine skippers really had little use for a permanently mounted searchlight but they did carry a handheld light to te conning tower at times for signalling purposes. It was able to be fitted with red, blue, and green glass filters for versatility and recognition signals.
A ship painted black to be stealthy and difficult to detect wasn't about to use a searchlight any more than it would use active sonar. Both would hasten the demise of the submarine and serve only as a director for enemy gunfire...