Perun's video on rocket artillery mentioned something I wasn't previously familiar with, the
XM70 developed in the late 1950/early 1960s. It straddles the line between being a rocket launcher and an artillery piece, apparently using a very small charge to get the projectile down a rifled barrel, at which point the rocket ignites. The ammunition is more of a traditional rocket than a RAP, and the whole thing's pretty lightweight at 3100 pounds for a 115mm launcher.
It carried 6 rounds in a pair of contrarotating 3-round revolver cylinders, and could fire all 6 in 2.5 seconds. Range was supposed to be 10 miles.
One thing I noticed while reading up on it is that while 115mm never caught on as an explosive round, it was used for rockets with payloads of VX and sarin. Those rockets were around 57 pounds each including a 10 pound payload and a 3 pound bursting charge, with a range of around 6 miles (lacking the gun boost to their initial velocity). The chemical rockets were the M55, and the XM-54 was the HE version, with firing tests of the XM-54 "gun boosted rocket" from the XM-70 occurring in 1959.
They don't really fit into any of the existing Twilight War scenarios, but they're still a bit of an interesting what-if.