In 2012, in one of my first posts, I explained a “Case for the Five Inch Gun.” All the reasons I outlined at that time have only become more salient over the last twelve years, but if the Hypervelocity Projectile (HVP–video above) becomes a real option, we will have even more reason to choose the 5″.
We could get many of the same benefits, and perhaps even more capability, by adding missiles to the USCG’s vessels and in some cases, we could put the capability on much smaller platforms, but the Coast Guard seems to be allergic to the idea of adding missiles, however small and innocuous, to their ships. The rationale seems to be we don’t want to appear threatening. I would argue that sometimes you just want to look capable.
If the Coast Guard is going to persist down this single gun/no missiles path, then the gun should be the best available in the US Navy inventory, the 5″/62 Mk45 Mod4 HVP or no HVP, assuming it would not look out of place, and it would not. Originally the 5″ Mk45 was designed as a direct drop in replacement for the 5″/38 single mount.
A modern 5″ gun would not be a radical change from the way Coast Guard Cutters have been armed in the past. The first Coast Guard cutters armed with 5″ guns goes back to at least USCGC Haida commissioned in 1921, which was armed with not one but two five inch guns.
Five inch guns remained a standard fit on large cutters until completion of the WHEC378 FRAM program in 1992. Over the intervening 71 years, at least 64 US Coast Guard cutters have been armed with 5″ guns.
Several classes had multiple three and five inch guns.

An aerial port view of the U.S. Coast Guard high endurance cutter RUSH (WHEC-723) underway during Exercise Brim Frost ’85.
A modern 5″/62 MK45 Mod4 on an OPC would not much look different from the 5″/38 on a 378, but it would provide much greater capability than the 57mm Mk110 which alone is not enough to meet the needs of an increasingly hostile geopolitical environment.















