"Schleswig-Holstein" and "Schlesien" then participated in the occupation of Denmark and invasion of Norway, respectively, in April 1940. Neither vessel saw action during the operations. Afterward, "Schleswig-Holstein" was again removed from front-line service and used as a training ship, while "Schlesien" resumed her ice-breaking duties. In March 1941, "Schlesien" escorted mine-layers in the Baltic. After returning from this operation at the end of the month, she became a stationary training ship in Gotenhafen. "Schleswig-Holstein" was briefly reactivated in early 1942 for ice-breaker service in the Baltic, and in May she accidentally collided with a shipwreck in the Gulf of Riga, forcing a return to Gotenhafen for repairs. The ship was thereafter reduced to training duties.