As part of their self-defence armament, QEC carriers were designed to carry four ASCG. They were not fitted when the ship was built and it was intended they would be added subsequently during one of the series of Capability Insertion Periods (between 2017-20). Official sources have confirmed it has been decided not to fit these weapons, at least for now.
Reaction amongst the tiny section of the population that concern themselves about such details has been overwhelmingly negative. There is an interesting PR/optics angle to this decision, there are many who already believe the aircraft carriers are inadequately protected and leaving off the ASCG may add further to this perception, whatever the operational justification.
In an ideal world of unlimited funding, the carriers would have the Sea Ceptor missile system and mount their full gun armament on the principle that you are unlikely to ever regret having too much firepower. (See broader discussion about aircraft carrier missile defences here) However, every weapon that is carried by a warship adds a cost in logistic support, maintenance and crew. The RN is always balancing finite resources and has concluded that investment in other means can provide an effective defence. RN weapon engineers know what they are doing and are not obliged to publish the detailed analysis behind such decisions. However naval sources have outlined some of the reasoning.
The ASCG have a role in air defence but their primary purpose, at least in the context of the aircraft carriers, is defence against small surface threats, in particular Fast Inshore Attack Craft (FIAC), small boat swarms and unmanned surface vessels. The development of this kind of asymmetric threat has been a growing concern for major navies over the last decade. For RN COs operating in the Gulf, the threat of attack by Iranian boat swarms has been a particular concern. With the procurement of the Martlet LMM and up to 20 of these missiles carried by a Wildcat helicopter, the RN, at last, has a guided weapon that can engage the small boat threat at range. For the CSG21 deployment, 4 Wildcats will be available, based on the two frigates and two destroyers. At least one, armed with Martlet, is likely to be held on deck at high readiness in higher threat environments. The Wildcats can also mount an M3M 0.5cal heavy machine gun, a powerful deterrent that can engage surface threats before they can get close to the high-value unit. Specialist Royal Marine snipers are also trained to operate from the Wildcat and are able to cripple the outboard motors of small craft with precision shooting.
The escorts of the carrier strike group do not normally operate right up close with the carrier but when transiting chocke points or in confined littoral waters they will be closed up forming a ‘ring of steel’ around the ship. Even if not engaged or fully eliminated by the Wildcat, any surface threat would be met by the escorts that have gun armaments of their own and would react immediately.
The ASCG can fire up to 200 rounds per minute out to around 4km. There is concern that if the 30mms were mounted on the carrier, there would be a fair chance of accidentally hitting one of the escorts. A high explosive 30mm shell will easily penetrate the light steel plate of modern warships and do considerable damage (RN warships experienced the effects of 20 and 30mm cannon shells fired by aircraft during the Falklands war). Although obviously something to be avoided, being hit by a stray Phalanx 20mm tungsten alloy round or a 12.7mm bullet from a 0.5cal would not be quite so serious.
The ASCG would be typically be controlled remotely from the operations room but the gunners would need to ensure the mounts are loaded and ready. There are some issues with ammunition degradation if left in on the mount for long periods and despite their remote or automated control, maintenance is manpower intensive
Any surface threat that escaped the attentions of the Wildcats and escorts would likely next be engaged by one of the automated Phalanx Block 1B CIWS on the carrier. The B1B upgrade was specifically intended to counter FIAC, helicopters, UAVs, USVs and small stealthy missiles, difficult to detect on radar. An Electro-optical camera and stabilised Forward-Looking Infra-Red (FLIR) camera is mounted on the left side of the radome and also allows the operator to visually identify targets in complex environments.
The last line of defence are the manually-aimed guns mounted on the upper deck and in the lower level gun ports. The RN has recently begun to equip its warships more regularly with the 50-cal heavy machine gun as it offers more hitting power than the Mini Gun and GMPGs that have been the mainstay until recently. These simple, robust weapons can be brought into action very quickly and are in widespread use by other navies. The Mini Gun and the GPMGs add a final layer of protection at close ranges.
Another type of close-in threat are UAVs (or ‘drone swarms’). An over-enthusiastic photographer managed to land a cheap consumer drone unchallenged on the deck of HMS Queen Elizabeth alongside in Invergordon (Aug 2017). Although there were some countermeasures in place they were not active. This event and the Gatwick Airport drone incident (Dec 2018), are relatively benign domestic examples of the threat, but cheap UAVs have also been successfully weaponised by ISIS and others in conflicts around the globe. The RN and the whole of UK defence have subsequently begun to take 24/7 counter-UAV defence much more seriously. Warships are now equipped with C-UAV technology, although details are classified and little is known about what this may comprise. It is likely that powerful soft-kill jammers that disable drones through electronic means are the primary defence.