Short story; war where speed of time changes with distance from front line

Question

Trying to remember a short story (most likely from the sixties). It starts with a soldier at the front line fighting an unknown enemy on the other side of the front line.

He then gets withdrawn and you realise that time is passing slower the further he moves from the front. He then spends years in peace away from the front, before being sent back to the front where only a short time (hours or days perhaps) have passed.

I seem to remember there was an inference that they were actually fighting against themselves, with their attacks coming back at themselves, which was perhaps the entire cause of the war, and an interesting critique on war. I can't remember if this all this was stated explicitly, or just left for the reader to infer.

Answer 1

David Masson, “Traveller's Rest”. Collected in The Caltraps of Time and various anthologies.

Another memorable detail is that the protagonist's name starts out as a single letter (“H”) and gradually lengthens as he goes away from the front line.

Indeed, the protagonist conceives the theory that the front line (“the Frontier”) is some kind of mirror, but his hierarchy dismisses the idea. It's obvious to the reader that the protagonist's theory is correct.