All Type 26 frigates will be equipped with the Mk45 Mod 4A Medium Calibre Gun, the latest version of a widely used weapon in the US Navy. This gun, found on over 280 warships across 11 navies, including those of Australia, New Zealand, Japan, and several NATO allies, represents a substantial improvement over the Mk8 4.5-inch gun, the Royal Navy’s standard medium-caliber armament since the 1970s. 

The Mk45 Mod 4 is a battle-tested, highly effective weapon designed for modern multi-mission warships. Developed with support from the US Department of Defense and the Royal Navy, it incorporates the latest advancements in gunnery technology, offering unparalleled adaptability to meet the Royal Navy's needs both now and in the future. 

According to the Royal Navy, the new gun is fully automated, safer, more reliable, and highly accurate. It can engage a wide range of threats, from aerial drones to fast-moving inshore attack craft, and is fully interoperable with NATO allies. Although the barrel is still to be fitted to HMS Glasgow, the gun will soon be capable of firing shells weighing up to 31.5 kilograms at speeds of up to 1,051 meters per second—three times the speed of sound. 

One of the gun's key features is its automated handling system, which eliminates the need for sailors to manually load shells. Instead, shells are pulled from a "deep magazine" to replenish the 20-round "ready to use" magazine, reducing the risk of injury and increasing operational efficiency. 

The Royal Navy describes the Mk45 Mod 4 as a top-tier medium-caliber gun, capable of performing under extreme weather conditions, day or night. It is easier to maintain, works seamlessly with allied forces, and boasts a reliability rate of 99.6 percent. 

The new City-class frigates, primarily designed for submarine hunting, are expected to join the fleet in the late 2020s and continue service into the 2030s. In addition to their anti-submarine role, these ships will also undertake a variety of other missions. They will feature adaptable mission bays to accommodate autonomous equipment, such as drones and mine-hunting systems, further enhancing their versatility in modern naval warfare.