21 round Rolling Airframe Missile launcher. Image credit Darkone via Wikipedia.
Since RAM is going on the FF(X) and could easily go on either the National Security Cutters and the Offshore Patrol Cutters, Thought I would pass along this short article about the system.
Chuck Hill's CG Blog 
Now . . . if you only had a non-rotating (fixed array faced) AESA radar to detect, track, and provide Fire Control . . . you would have a mini-Aegis!
The 21-cell size instead of 22 or 24 cells is odd (in more ways than one, not just an odd number but also strange). In this age of swarms of drones and swarms of missiles, every missile you can add to the ship counts. They could have easily added at least one more missile on the top row (making it a row of four missiles) just by rounding-off the corners on the top row like they did on the bottom row, instead of those strange diagonal cuts on the top row that limit it to three missiles. That would make it hold 22 missiles, twice as many as the SeaRAM’s 11 missiles.
And it appears that the third and fifth rows hold only three missiles just due to the hinges getting in the way, but that seems a thoughtless design. They could have put four missiles in those rows if they either modified the hinges or widened the launcher by just a couple inches.