From Mud and Blood official Wiki
"D-DAY Ribbon. Score a 100 wave game the 6 of June and You will start the game with one more TP."— Official game quote
D-day, The day when Allied forces landed in Normandy France and began the end of the war. The U.S military has decided to commemorate this astonishing feat of logistics and skill by giving the commander who reaches 100 waves on June 6th an extra TP on every new game they start, and also respect from others.