At a time when the US Navy is looking to field a light frigate variant of its troubled Littoral Combat Ship, with a main battery of a single 57mm Mk100 automatic gun, our cousins across the pond, the Royal Navy, have decided that their next frigate, the Type 26 Global Combat Ship, will be armed with a 5” gun.
For generations, the primary gun of the Royal Navy has been the 4.5” gun, in various mounts. In contrast, the main US gun has, since well before World War II, been a 5” gun. But the last class of US frigates, the FFG-7 Oliver Hazzard Perry class, dating back to the late 1970s, were armed with a single automatic 3” gun. And as noted, the follow on to the FiGs is armed with a 57mm.
The gun the RN chose for the Type 26 is an American gun, the Mk45 Mod 4. The Mk 45 first entered US service in the mid 1970s on the Spruance class destroyers and the Tarawa class amphibious assault ships. That variant, still in use on a great many ships of the Arleigh Burke class destroyers, had a 54 caliber barrel. That is, the bore (5”) time 54, for a barrel length of 270 inches, or about 22 and a half feet.
The Mod 4 variant of the Mk 45 has a barrel 62 calibers long, for 310 inches, or just shy of 26 feet. That longer barrel gives the gun a significant boost in range, and the more modern gun also has the ability to fire extended range projectiles, and growth potential to fire guided projectiles. It may not be the 16”/50 of an Iowa battleship, but it is a decent weapon.