The type 7C/42 was designed for faster surface speed and deeper diving depths to avoid depth charges. This was done by engine modifications and adding a second stage super charger to increase engine speed. This resulted in a lengthened boat by 31.5 metersfor this modification plus 1.5 meters forward to counter balance this weight. New top speed increase was 1.6 knots faster than before. The pressure hull diameter was increased by 300 MM and constructed of KRUPP 28MM "CM-351 ärmored steel,normal diving depth was now 656ft and crush depth was now 1,640ft. The saddle tanks were also widened by 350MM to increase bunker storeage for extened range. The friction clutch was replaced by a hydrolic clutch . A dehumidifier was also added for the crew comfort when sailing in the tropics etc.. None were laid down nor ever completed.