When the Germany invaded the Netherlands, France, Norway and Greece several enemy ships fell into the hands of the Kriegsmarine. Most of them were smaller vessels like patrol boats, gunboats, torpedo boats or destroyers. Several of the torpedo boats and destroyers were put into service for the Kriegsmarine again, while some older coastal defense ships were modified to floating anti-aircraft batteries.
In addition to the already operational ship, Germany also took over foreign shipyards with a number of ships still in construction. Some of them were tried to be completed (like the French cruiser DeGrasse
which should be completed as an aircraft carrier), but in most cases those ships were still under construction at the end of the war, a few were were later commisioned after the war.
After the surrender of Italy in 1943, Germany captured all the ships of the Italian Navy that were stationed in the German controlled part of Italy and put them into service as Kriegsmarine ships. Due to the increasing fuel shortage, this relative high number of ships did not see much operations at all.