AFP - The image of American GI's who landed in Normandy in June 1944 has long been choreographed as one of handsome young men liberating an occupied country. A new book, however, paints a darker picture.

Far removed from accounts of selfless derring-do, many US soldiers were viewed by the French as sex-obsessed thugs who had been promised an "erotic adventure" -- a mission that was fulfilled, much to the chagrin of locals.

That this happened is not a secret in the Normandy region "but it's a big surprise for the American audience," Mary Louise Roberts, author of "What Soldiers Do: Sex and the American GI in World War II France," told AFP.

Roberts, a history professor at the University of Wisconsin, Madison, wrote the book, which will be released next month, after extensive study of wartime archives in France and the United States.

Her research seeks to debunk an "old myth about the GI, a manly creature that always behaves well," she says, noting that sexuality, prostitution and rape were all methods used by Americans to "assert their power on the French."

While the US press described the liberation as a tale of romance -- backed up by photographs of American soldiers kissing young French women -- more often than not the reality was less giddy.

A local saying summed up the problem: "With the Germans, the men had to camouflage themselves -- but with the Americans, we had to hide the women."

Debauchery, lawlessness and disturbing tales of institutional racism are cited. "The GI's were having sex anywhere and everywhere," Roberts says.

In the cities of Le Havre and Cherbourg, bad behavior was common. Women, including those who were married, were openly solicited for sex. Parks, bombed-out buildings, cemeteries and railway tracks were carnal venues.

But the sex was not always consensual, with hundreds of cases of rape being reported.

Le Havre's then mayor, Pierre Voisin, complained to Colonel Thomas Weed, commander of US troops in the region, about the GI's behavior, according to documents cited by Roberts.

"The people could not go out for a walk without seeing somebody having sex," she says, and though US officers denounced such behavior publicly they did little to curtail it, according to the historian.

Roberts does not neglect the fact that US soldiers did act with bravery and much heroism, and mentions how such behavior attracted French gratitude.

Her book, however, recounts propaganda purportedly meant to motivate young Americans to fight a war in a country they hardly knew but which had the more immediate effect of feeding the soldiers' sexual desire.

Life magazine described France as "a tremendous brothel inhabited by 40 million hedonists," while the Stars and Stripes newspaper published a series of suggestive French phrases.

"You are very pretty," "Do you want a cigarette?" and "Are your parents at home?" were among the helpful hints.

"Once aroused, the GI libido proved difficult to contain," Roberts writes.

The book also addresses disturbing claims of racism within the US military, with black soldiers facing a disproportionate number of rape charges.

Documents dated October 1944 show that of 152 troops facing charges, 130 were black, which Roberts says shows "the US army demonstrated a deep and abiding racism." The French were also "quick to point the finger at black GI's."

Almost 70 years on, Roberts says she does not seek to rewrite history, but instead aims to put the French "back in the picture," and recount the Normandy campaign "as a human experience, not just an empty 'heroic' story."