It doesn't of course mean an entertainment for the troops but is army slang for battle. His own recent reading has left its mark on the poem. This is a graphic account of a Europe at war with the dead looking down on terrible scenes of crawling things dwarfed to the size of insects and worms. The genesis of THE SHOW, therefore, is obvious, and we can be sure that when writing it Owen did not exaggerate.
Personal involvement is clear from the outset.
My soul looked down from a vague height, with Death. Almost certainly to shock. By using the plain language of specifics and avoiding abstractions. But surrealism is not the whole story. Dawn follows the gloom that is night's darkness, but, ironically, the gloom that is despair, that remains.