The Outfit

After you destroy the second Nazi outpost on level 2 get into a Nazi tank at the second Nazi outpost if your not in a tank then on your way to the destroy the Nazi HQ objectives you will see a train back up but the medal oppertunity has to come up then you can destroy the train car and get the achievement. Destroying the train car before the medal oppertunity comes won't get you the achievement.

To get the medal oppertunity you have to wait for the train to back up then stop at this cannon. Shoot at the train car behind the locomotive then the oppertunity comes up to shoot the train car behind the locomotive. Shoot the train car until it blows up then you get the achievement.

When going through this game which I am highly recommending doing is using the Xbox Achievements road map made by CienPR, when you hit each level of the story just hit CTRL+F on the page and type the Mission you are on, and you will find the achievements you need to look out for and how to do them on each mission. There is about 2 each mission, and there aren't any videos which I would be posting if I could find some, but I guess this game isn't popular enough.

Again credit goes to CienPR, good luck and have fun

Road Map:

http://www.xboxachievements.com/game/the-outfit/guide/#

The other guides are fine, but it's important to note that you must take out the train car on the second train that backs up. I kept trying to destroy the first train car I encountered which was wrong.

Make sure to have a Nazi Tank before you do this. After destroying the second outpost, keep progressing through the level until you see the SECOND train back up. You will see a small cannon on the left side of the train. Lightly pepper the train car with machine gun fire until you see the medal opportunity pop up. At this point, use your rocket fire and you should get the achievement once the train car (troop car) is destroyed .