From Wikipedia: 

A Japanese army officer is traveling down a deserted road at dusk, on his way back home from fighting in the war. He comes to a large concrete pedestrian tunnel that seems to go on forever into the darkness. Suddenly, an angry, almost demonic-looking anti-tank dog (strapped with explosives) runs out of the tunnel and snarls deeply at him. He proceeds with his walk, afraid, into the tunnel. He comes out the other side, but then witnesses something horrific — the yūrei of one of the soldiers (Private Noguchi) whom he had charge over in the war comes out of the tunnel behind him, his face a light blue, signifying that he is dead.

The soldier seems not to believe he’s dead, but the officer convinces him and the soldier returns into the darkness of the tunnel. Just when he thinks he’s seen the worst, the officer sees his entire third platoon marching out of the tunnel. They too are dead, with light blue faces. He tries to convince them that they’re dead, and he expresses his deep-seated guilt about letting them all die in the war. They stand mute, in reply to his words. He then orders them to about face, and then march back into the tunnel. Lastly, we see a second appearance of the hellish dog, from the beginning of this dream.

This is one of three “nightmares” featured in the film.

Akira Kurosawa’s long time friend Ishiro Honda may have helped to direct, or have directed this piece entirely. The two always spoke of filming a story of a dead soldier returning from war.