A new book claims that after landing on the Normandy beaches in 1944, and being plunged into battle over the following months, many of the soldiers struggled to deal with what they had experienced.
Some had been fed a story by US propaganda services that battling Nazi Germany was a tale of romance, supported by photographs of American soldiers kissing young French women, but for many there was a darker side.
"The real trouble began in the summer of 1945," said Mary Louise Roberts, author of What Soldiers Do: Sex and the American GI in World War II France.
"The GIs were exhausted and traumatized. They drank a great deal, and suffered from what we now call post-traumatic stress syndrome.
"Most of the sexual violence they inflicted on the French people came from their own attempt to deal with their war experiences."
Mary Louise Roberts, a history professor at the University of Wisconsin, was interested in knowing how the Americans and the French viewed each other at this crucial moment in history.
And her work started with Stars and Stripes, a US military newspaper widely read in France by the GIs.
"I found that the US military had eroticized France as a nation of beautiful women ready to offer kisses for their liberation," said Mary Louise Roberts.
In researching her book Mary Louise Roberts called on many sources and visited 18 archives on both sides of the Atlantic.
"Mainly I drew on memoirs and journals of the Normandy battle, police reports, US military and juridical documents and papers of local French officials in Normandy," said Mary Louise Roberts.
Bad behaviour was common in larger cities such as Le Havre and Cherbourg, with many women openly solicited for sex, and hundreds of cases of rape being reported.
In her book Mary Louise Roberts recognises the bravery of the troops and the heroic acts of many, however her findings have still caused some to criticise her findings.
"The book has upset many people," said Mary Louise Roberts. "I have not heard from veterans associations as groups, but I have heard from individual veterans from more recent wars, Korea, Vietnam and Iraq.
"Some of these letters are damning and ugly. But still other veterans have offered me very insightful views from their own experience as soldiers."