Declassified documents held by the investigative agency reveal the FBI received rumours of Hitler's survival just five months after his death on April 30, 1945.
US spooks received information claiming the Nazi leader had fled Germany via U-boat in the dying days of the war as the allies pressed on Berlin.
It is said Argentine officials welcomed Hitler and he remained hiding out in the foothills of the Andes.
FBI files are dated September 21, 1945, just two weeks after Japan surrendered following the dropping of the A-bomb and the official end of World War 2.
History accepts Hitler shot himself aged 56 in his Fuhrerbunker on April 30 that year - almost exactly 74 years ago this week.
And should Adolf have survived the war, he would have just celebrated his 130th birthday this Saturday.
FBI files held of the bureau's officials website reveal the investigation into claims of Hitler's survival went right to the top of the bureau - being considered by director John Edgar Hoover.
Numerous letters between Hoover and his underlings reveal they passed information to military intelligence after receiving the tip-off.
The heavily redacted data packet reveals claims Hitler arrived in Argentina two and a half weeks after the fall of Berlin.
Two submarines are said to have pitched up on the shores of Argentina, before they were then led away on horseback into the foothills of the Andes.
The information is said to have come from a source met by an FBI agent in Hollywood who was seeking "immunity from being sent back to the Argentina".
There's a series called Hunting Hitler that looks at the evidence of Nazis and possibly Hitler making it to South America.