NERVA has about 250 kN of thrust at 841 seconds of specific impulse.
Merlin 1D has about 1000 kN of thrust at 311 seconds of specific impulse.
That suggests NTRs have around 4x less thrust, but around 2.7z more efficiency than chemical rockets. At a large enough scale craft, the weight of the engine could be considered irrelevant. But for smaller crafts, the Merlin has a thrust to weight ratio of 184:1, whereas NTRs only ever achieved 7:1 (they hoped to get up to around 35:1 eventually).
I imagine the thrust to weight could be substantially improved by making lightweight reactors, but I’m wondering if anybody knows anything about concepts for higher thrust NTRs?
https://en.wikipedia.org/wiki/NERVA
https://en.wikipedia.org/wiki/SpaceX_Merlin
The NTP applications I’ve seen rely on chemical rockets to get the vehicle into space, and then the NTP to maintain acceleration after the chemical is exhausted. The chemical engines are never going to store enough propellant to keep firing for very long, but the NTPs can theoretically maintain acceleration for, say, a whole journey to Mars, flipping around to decelerate halfway. Even with the smaller thrust, a vehicle doing this can get up to a nontrivial percentage of light speed.
but for a hypothetical combat scenario, you’d want something (maybe extra chemical boosters) for maneuvers