Mud and Blood Cross
One of the hardest and most distinguished medals. Survive an average of 100+ enemy waves per mission to the 50th mission and get this award. The reward is great, though. A 9-exp soldier ranks up really quickly (with 1 exp!).
Note: This Medal requires you to survive an Average of 100 waves. This means that you don't have to get 100 waves per game, but on your 49th deployment, you must have 5000 waves under your belt. This means you can have games which end before the whistle blows (wave 10-30) as long as you make up for it with High wave games (120+).