Devin Monnens pointed me at an obscure version of PDP-1 Spacewar as seen at the Holloman Air Force Base (New Mexico) in 1966. John W. Andrews reported a description to “The Gamesman” magazine, who published it in Issue 4, Dec. 1967 (pp 31-32). An archived copy is available here: https://archive.org/details/The_Gamesman_4-1967-12/page/n31
The most interesting feature is probably the changed setup with the spaceships facing inwards, towards the central star, allowing for a bit of variety in opening tactics as compared to the standard game. Moreover, exhaust flames decrease with fuel consumption, doubling as a fuel gauge. (There had been discussion among users, whether or not the acceleration would also decrease, while fuel is burnt. I guess, this may have rather been a false impression.) Moreover, there’s a handful of additional torpedoes for each ship and the central gravitational star apparently kills on contact in the default settings. Even more thrills provides the last feature, ships colliding with background stars when re-entering from hyperspace. While this rarely occurs, it’s yet another thrill, knowing that this might happen.
So, in order to explore this, I gave it a shot, hacking the original PDP-1 assembler code. (While most features could have been implemented by a simple patch tape, the hyperspace re-entry feature requires an additional lookup table for the current positions of the constantly moving background stars of the “Expensive Planetarium” and would have probably required access to the source code.)
See/try it here: https://www.masswerk.at/spacewar/?v=spacewar4.1hafb