Total Annihilation was the first to have projectile physics for artillery and other weapons. One could actually have, for example, an artillery projectile in mid-flight accidentally collide with an aircraft.

[EDIT] Not mentioned on the BAR front page but also pioneered in TA was wreckage. Destroyed units left wreckage behind that had to be navigated around or fired upon to clear a path. Wreckage could also be scavenged to recover the material used to construct them, allowing the construction of more units. In the race to build enough infrastructure to overwhelm the enemy, this could be the difference between life and death.