During and immediately following World War II Ellis Island was used to intern German merchant mariners and enemy aliens - American civilians or immigrants detained for fear of spying, sabotage, etc. Some 7,000 Germans, Italians and Japanese would be detained at Ellis Island. It was also a processing center for returning sick or wounded U.S. soldiers, and a Coast Guard training base. Ellis Island still managed to process tens of thousands of immigrants a year during this time, but many fewer than the hundreds of thousands a year who arrived before the war. After the war immigration rapidly returned to earlier levels. Noted entertainers who performed for detained aliens and for U.S. and allied servicemen at the island included Rudy Vallee, Jimmy Durante, Bob Hope, and Lionel Hampton and orchestra.
The Internal Security Act of 1950 barred members of communist or fascist organizations from immigrating to the United States. Ellis Island saw detention peak at 1,500, but by 1952, after changes to immigration law and policies, only 30 detainees remained.
One of the last detainees was the Aceh separatist Hasan di Tiro who, while a student in New York in 1953, declared himself the “foreign minister” of the rebellious Darul Islam movement. Due to this action, he was immediately stripped of his Indonesian citizenship, causing him to be imprisoned for a few months on Ellis Island as “an illegal alien”.