The Royal Navy's Gun Revolution

A training exercise for a 30mm DS-30B naval cannon. In this case its on a UK Royal Fleet Auxiliary vessel 12 years ago. Same weapon used on HMS Diamond - details below.
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The Royal Navy (RN) of the United Kingdom has always been a gun-armed Navy, since it was founded as the 'Tudor Navy' by Henry VIII in 1485. While the 'missile age' of naval warfare has diminished the importance of gun weapons as offensive weaponry, recent events in the Black Sea and the Red Sea have reinforced the importance of guns for warship self-defense.

The UK Defence Journal recently published a question formally asked in the UK parliament about the UK's air defence assets. This has confirmed an issue that was brought up by Navylookout.com in an after-action report of the Type 45 Daring-class air defence destroyer HMS Diamond's engagement of Houthi UAVs, ASCMs and ASBMs in January 2024 - that the 'main-gun' of RN destroyers and frigates, the British 4.5-inch (114mm) Mark 8 naval gun, does not have anti-aircraft capabilities, as Naval Lookout observed: 

"4.5-inch Mk 8 gun is now really only useful in the Naval Gunfire Support role in relatively benign environments. The software support for its original limited anti-air capability was withdrawn some time ago as a cost-saving measure."

I've been curious about the resurgence of naval guns as a counter UAV/USV weapon, especially as there are now proximity and guided projectiles for 30mm, 40mm, 57mm, 76mm and 5-inch (127mm) naval guns. 

Smaller 30mm calibre gun ammunition are much more economical than expensive SAMs for knocking out small cheap swarms of UAVs and USVs, but a larger calibre weapon can engage targets at a further (thus safer) distance - the Danish frigate Iver Huitfeldt fired 50-100 76mm rounds against an approaching drone when its ESSM missile system failed for 30 minutes - though the resulting weapons failures were actually the result of long-standing issues known to the Royal Netherlands Navy.

HMS Diamond has engaged Houthi airborne targets with its Sea Viper (48 Aster 30/15/1NT missiles). On April 24, 2024 it was HMS Diamond's Sea Viper system that shot down a Houthi ASBM, a first for the Sea Viper/Aster missile system (see final paragraph here). HMS Diamond's 2 x 30mm DS-30B cannon and 2 x 20mm Phalanx 1B close in weapon system (CIWS), have also been seen action, and these guns are mounted on the flanks of Daring-class Type 45 destroyers like HMS Diamond.

image: Seaforces.org. A 30mm DS-30B autocannon and 20mm Phalanx Block 1B aboard a Type 45 Daring class Destroyer ---

The DS-30B is a stabilized Oerlikon KCB 30mm cannon with a pedestal-mounted 30mm automatic cannon that can fire proximity fused ammunition. Here is a report of 5-inch fused ammo for the USN as an example of this concept. The UK RN has not disclosed if it uses such fuse ammo. The KCB has an effective range of 3km, while the Phalanx's is 1.5km, now considered marginal against supersonic threats. 

To upgrade its ships' self-defence capabilities against asymmetric threats, the RN has experimented with adding Marlet LMM (Lightweight Multirole Missiles) to its DS30M Mk2 mounts (which use the Bushmaster 30mm canons) but this has not been successful. 

The latest news is that the RN is going Star Wars, by outfitting many of its ships with the 50kW Dragonfire Lase Directed Weapon (DEW) from 2027.

The Type-45 Daring Class entered Royal Navy service in 2009 and is scheduled to retire in 2038, when the planned Type 83 destroyer replaces them. The RN's Type 23 Duke-class frigates are also retiring by 2035, which means that the Royal Navy is phasing out the 4.5-inch naval gun, so restoring its capabilities against aerial targets is not a priority.

The Type 26 Gasglow-class frigates, the first of which is now 65% complete, has switched to the 5-inch (127mm) Mark 45 Mode 4 naval gun, which is used by the US Navy and the Royal Australian Navy and is capable of firing programmable and guided munitions.