From September–December 1939 U-boats sank 221 ships for 755, 237 gross tons, at the cost of nine U-boats. Only 47 merchant ships were sunk in the North Atlantic, a tonnage of 249,195. Dönitz had difficulty in organising Wolfpack operations in 1939. A number of his submarines were lost en route to the Atlantic, through either the North Sea and heavily defended English Channel. Torpedo failures plagued commanders during convoy attacks. Along with successes against single ships, Dönitz authorised the abandonment of pack attacks in the autumn. The Norwegian Campaign amplified the defects. Dönitz wrote in May 1940, "I doubt whether men have ever had to rely on such a useless weapon." He ordered the removal of magnetic pistols in favour of contact fuses and their faulty depth control systems. In no fewer than 40 attacks on Allied warships, not a single sinking was achieved. The statistics show that from the outbreak of war to approximately the spring, 1940, faulty German torpedoes saved 50–60 ships equating to .