https://www.uboat.net/ops/agents1942.htm

Operation Pastorius was a failed German military intelligence (Abwehr) mission intended to sabotage the American war effort and demoralize the civilian population. The Abwehr recruited eight German residents (two were US citizens) who had once lived in the United States and trained them in the manufacture and use of explosives, incendiaries and delayed timing devices. 

On the night of June 12, 1942, the submarine U-202 disembarked four of the saboteurs at Amagansett, Long Island New York. After burying their uniforms and explosives in the sand, one of the members George John Dasch was  discovered by an unarmed Coast Guardsman whom he threatened and bribed with $260 to remain silent. After the Coastguardsman reported the encounter, an armed patrol arrived too late to catch the  Germans, who had taken a train to Manhattan. When the saboteurs’ buried equipment was found, the FBI initiated a manhunt.

On June 6, U-584 landed the other four-member German team at Ponte Vedra Beach, Florida. After changing into civilian clothes, they boarded trains to Chicago and Cincinnati. The two teams planned to meet on July 4 in Cincinnati to coordinate their operations.

Realizing that the mission was compromised by the encounter with the Coast Guard, and disliking Nazism, Dasch and another team member Ernst Burger (an American citizen) secretly decided to defect to the United States. Dasch took a train to Washington. D.C. and turned himself in at FBI headquarters. Within two weeks, Burger and the other six team members were arrested.

On August 1, 1942, a specially-convened military tribunal found all eight defendants guilty of espionage and sentenced them to death.  Because the information they provided enabled the capture of the other Operation Pastorius team members, FDR commuted Burger’s sentence to life imprisonment and Dasch’s to 30 years. The others were executed.

The only other WWII German sabotage mission to the USA occurred in November 1944 when the U-1230, dropped two spies off the coast of Maine to gather intelligence and sabotage the Manhattan Project and munition factories. Both men were swiftly captured by the FBI and received prison sentences rather than execution.

Read more:   uboat.net – U-boat Operations – German saboteur landings in June 1942.