Here's a link in the words of one more knowledgeable than myself.
http://www.i-mef.usmc.mil/msc/1mardiv/3bn5mar/history.htm
Long story short, the 5th Marine Regiment was awarded a French Fourragere for its valor in France. One of the more famous battles being the Battle of Belleau Wood where the Marines were given their title of "Teufelhunden", which translates to Devil Dog. The Fourragere is the highest military award that the French can award a specific unit, and those in the 5th Marines are proud of this fact and still laud it to this day.
Now known as the "Darkhorse" battallion, 3/5 is currently where I am stationed and I am still surprised by how rich in history and tradition they are and continue to be. They have been deployed to Iraq for 3 straight times, taking part in OIF I, Operation Phantom Fury (Battle for Fallujah), and on their last deployment to the Al Anbar province for a more police-like effort. I've yet to go on a deployment, and the next one that we are slated to take is on the 31st Marine Expeditionary Unit to Okinawa, Japan. Anything can happen though, and we'll be the QRF for the Pacific from Aug. 07 to Jan. 08.
3/5..."Get Some!"
