Eight German agents came to our shores in the late spring of 1942 and brought explosives with them to do harm, They came in two parties and all were known to each other. All spoke English and most had lived in the USA. Two were naturalized US citizens. Team members Joseph Dasch and Ernst Burger (who had spent time in a concentration camp) decided to betray the mission and Dasch went to see J. Edgar Hoover. Within less than two weeks, all were in Federal custody.
FDR decreed that the agents not be subject to civilian courts but to a secret military tribunal. Such tribunals had not been used since the Civil War. Other rules were waived in that a vote of two thirds of the members of the tribunal would establish guilt and allow imposition of the death penalty.
All admitted their guilt. The trial was rather lengthy and it took three weeks to reach guilty verdicts and impose death sentences on all eight. Several days later, six of the group were electrocuted in Washington DC.
Dasch and Burger were saved from the electric chair and ordered imprisoned. Both were ordered released by Harry Truman and returned to Germany three years after the end of the war. Dasch wished to stay in the United States but this wish was never granted. None of the agents had carried out their plans and some seemed reluctant to so. We were at war so no major complaints about short-circuiting the judicial process were heard.
Details of the case may be found under Ex parte Quirin. Chief Justice Rehnquist dealt with the matter in great detail in his 1998 book: All the Laws but One : Civil Liberties in Wartime. New York: William Morrow & Co.. ISBN 0-688-05142-1.
We were at war and they did come to blow up America. The incident was made into the 20th Century Fox 1943 film “They Came to Blow Up America”. There are some factual errors in the film. They added a ninth saboteur.
German agents were more effective during World War I with the massive ‘Black Tom’ explosion in New Jersey. The blast even damaged the Statue of Liberty. The major act of possible WW II sabotage was the burning of the liner Normandie in NYC. The ship was to become a troopship and many believed that the arson was a mob hit to encourage the use of mobsters to maintain waterfront security.