What was the first ever FPS with secondary fire?
Solution 1:
My answer is Star Wars: Dark Forces in 1995.
The game is often referred as a Doom clone, but it also added gameplay features that were uncommon to the first-person shooter genre at the time of release.
This comes from its original manual:
For combat, the player may use fists, explosive land mines and thermal detonators, as well as blasters and other ranged weapons. All weapons, with the exception of the fist, have a secondary mode which makes it have a different effect than in primary mode.