The most daunting problem for Germany in protecting an invasion fleet was the small size of its navy. The "Kriegsmarine", already numerically far inferior to Britain's Royal Navy, had lost a sizeable portion of its large modern surface units in April 1940 during the Norwegian campaign, either as complete losses or due to battle damage. In particular, the loss of two light cruisers and ten destroyers was crippling, as these were the very warships most suited to operating in the Channel narrows where the invasion would likely take place. Most U-boats, the most powerful arm of the , were meant for destroying ships, not supporting an invasion.