Sergeant Reckless is a song by Marie-Lynn Hammond (anyone remember her from her days with Stringband?) about a small sorrel mare named Sergeant Reckless after the recoilless rifles used by the gunners. The song is sung from the POV of a fictional young Marine whose battalion acquired the mare to help carry ammunition to the gun crews. It's one of the songs on Hoof Beats, Marie-Lynn's new horse-song CD.
I was almost certain I'd previously posted the wonderful story of this real life Korean war hero but can't find it. Here's a video about Reckless:
You can also read more about Sgt. Reckless here.