While Bowery claims to have the first documented 3D first person game, this claim does not go entirely unchallenged. Maze War, also known as The Maze Game, Maze and Maze Wars, was a program developed at the NASA/Ames research center in the summer of 1973 that could also be a contender for the title of the first 3D first-person game.
Maze War was aptly named, consisting of a maze constructed of polygon walls at 90 degree angles, through which a player could navigate and then shoot at other players. Maze Wars included technical innovations that were not present in many of the early PLATO titles. While the ships in Spasim were wire frame polygons that one could see through, the walls of the labyrinth in Maze War used a set of algorithms to eliminate any polygons that would not be visible to the player, lending an impression that the walls were solid. This is a technique that would not be seen again for some time, particularly not in the home computer market.
A History and Analysis of Level Design in 3D Computer Games Sam Shahrani