AFAIK what the military has been researching are large (naval) railguns. Coilguns are a novelty with minimal utility (note that the actual principles involved in them are used in real things, but mostly for accelerating things along rail systems, not as guns or cannons), but railguns have some promise in pushing the upper limit of what artillery can do (and AFAIK what they were focused on was specifically a hybrid system that would launch a shell with conventional propellant into a railgun barrel that would then accelerate it even harder) because they can get things moving faster than gas can expand and put more force on a projectile than conventional propellant alone could without having a building sized barrel to accommodate the force.

Ultimately the project made a big fixed emplacement that could launch a projectile faster and harder than any other system, but which was both logistically infeasible due to it rapidly destroying its own barrel (a seemingly intractable problem with railguns is that at high power levels the surface of the rails oxidizes and the rails themselves can warp), and obviated by missiles largely replacing the role of artillery along with "what if we could put a single shell somewhere near a target even faster than a missile, once, and it would take an entire ship dedicated to this task" turning out to not be as useful a niche as sci-fi brained military officials thought it would be fifty years ago.