Kryptopolitans and Barry picks up a gun for the war effort.
These are from The Brave and the Bold #28 in which Barry volunteers for an experiment and accidentally travels back in time to the Battle of the Bulge then joins the Blackhawks in their fight against the Germans.
Barry's leg is broken when he awakes after blacking out. Some Nazis spot him and fends them off by pelting bricks at them.
Barry is reluctant to help the Blackhawks kill even though it's WWII and he would be fighting Nazis and he doesn't seem to have a problem with only possibly killing them with bricks to the head at super speed. Since Barry vowed to never kill while wearing his Flash "uniform" he takes it off and puts on an American soldier's uniform to help the Blackhawks just until his leg heals.
The issue ends with Barry putting on the Flash suit, his leg healed, and returning to the present via the rift his experiment created, but not before Blackhawk says, "Go with God, son."
And now for something completely different.
That was posted on Jimmy Palmiotti's blog. It was drawn for fun at a con by Amanda.