As I mentioned earlier it was for M/S Karskär and sister ship M/S Rönnskär very first trip with cargo, human cargo, the survivors. Most of them were Holocaust survivors from the concentration camp Bergen-Belsen. Both ships were built during the WW II at the Öresund Shipyard and to be accepted for the White Boat mission they had to be modified for that. The need for modifications was big as both were strictly built as pure cargo ships. The scope of changes appears in a decision by the Swedish Navy Administration on June 13, 1945: In existing spaces on the middle deck and in the hold, 129 double cots were to be installed, thus giving a total of 258 beds intended for patients and 14 single beds for Red Cross personnel.
Furthermore, 15 field toilets were to be added (and a urinal arranged). Behind the superstructure would be a temporary kitchen with a field stove on beams and cupboards, drawers, and tables. The deck lighting would be supplemented with "solars" (large deck lamps). The stock of life rafts and life belts would be supplemented. The work was to be carried out at the Öresund Shipyard.
M/S Karskär did 10 trips between Lübeck and ports in Southern Sweden, Malmö, and Trelleborg.