From H. Montgomery Hyde's Room 3603: The Incredible True Story of Secret Intelligence Operations During World War II, page 69:
''...the famous 'Black Tom' explosion in Lower New York Harbour in July, 1916, when thirty-seven loads of high explosives, several warehouses, a dozen bargers and chips and a whole railway station and yards were blown up in one terrific detonation. Had the Germans possessed a sabotage operation in America under the efficient direction of a man like Captain Von Rintelen as they did in the First War, the precautions taken by B.S.C.'s Security Division would have been much more hampered and less effective than they were proved to be in the event.
Of upwards of 20,000 cases of suspected sabotage which the F.B.I. investigated during the Second World War, Hoover claimed that not a single case of enemy directed sabotage was established. For the most part, they were industrial accidents caused by fatigue, carelessness, horseplay among the workers, and occasionally spite.
The only attempted at active sabotage which the Germans made after America had entered the war was a complete fiasco. Early in 1942, Canaris received instructions from Hitler to cripple the American production of aluminium. Since no organization for sabotage existed in America at that time, agents had to be recruited and sent from Germany, an operation in whose success it appears neither Canaris nor Lahousen had much faith. Nevertheless the Fuehrer's orders had to be obeyed, and accordingly on May 28, 1942, eight agents were landed by submarine in groups of four at two different points on the eastern American seaboard.
Two of the prospective saboteurs promptly gave their comrades away to the FBI, thereby saving their own skins, while the remainder were rounded up and in due course went to the electric chair. "It was the biggest failure that ever occured in my section," General Lahousen recalled with a sigh after the war was over.