Big crowds gathered to wish "bon voyage" to the painstakingly recreated tall ship Hermione, leaving from Ile d'Aix, in southwest France, for the east coast of the United States.
The French and American flags were raised on the wooden frigate and crew members made last minute preparations for their Atlantic crossing retracing the voyage 235 years ago of General Lafayette, who won fame for rallying America's rebels fighting for independence from Britain.
Earlier, US President Barack Obama sent a message stressing "friendship between the two countries," according to the head of the Hermione-Lafayette project, Benedict Donelly.
The US consul in the nearby city of Bordeaux was to read out the message at the ceremony.
Then, after a fireworks display, the ship was to set sail at 2030 GMT, with a first stop due in the Canary Islands, before continuing across the Atlantic Ocean.
Some 80 crew members will sail the three-masted 65-metre (213-feet) ship along the route to Boston made by French General Gilbert du Motier -- the Marquis de Lafayette -- to bolster revolutionaries fighting for an independent United States.