In focus: the 127mm Mk 45 gun that will equip the Type 26 frigates

When the first Type 26 frigate becomes operational it will introduce another gun type to Royal Navy service. BAE Systems’ renowned Mk 45 127mm (5-inch) gun is already proven with navies worldwide and will be a considerable upgrade on the existing medium calibre gun. Here we look at this weapon in detail.

In naval use the, 5-inch gun are seen as having a good balance of firepower in relation to its size, typically installed on destroyers and as secondary armament for battleships. Apart from an ancient muzzle-loading cannon used in the late 19th century, the RN has not previously employed guns of exactly this size. The closest was the twin QF 5.25-inch Mark I gun (50 calibre) which was a dual-purpose anti-aircraft anti-ship weapon brought into service during the second world war.

Since the 1970s, the Vickers Mk 8 113mm (4.5 inch) 55-calibre gun has equipped the majority of RN surface combatants. This lighter mount replaced the twin QF Mark V 45-calibre guns (later renamed the Mk 6 ) which equipped most destroyers and frigates built in the 60s. After overcoming initial reliability issues, the Mk 8 has matured into a solid performer with a maximum rate of fire of 26 rounds per minute, firing a 36.5 kg HE ER (extended range) shell up to about 27.5 Km. The original Mod 0 mount was substantially upgraded to Mod 1 standard from 1998 with electric motors replacing most of the hydraulic actuators and servos, reducing weight and increasing safety and reliability. The round fibreglass gun shield was replaced by a more angular housing designed to reduce radar cross-section, its appearance giving rise to the nickname ‘Kryten’ after the mechanoid character in TV series Red Dwarf.

In 2004, United Defence (before being taken over by BAES in June 2005) proposed the Mk 45 Mod 4 for the Type 45 destroyer but was rejected as too expensive. In response, BAES proposed an upgrade to the Mk 8 to a heavier calibre 155mm (6.1-inch) gun which would have given the RN commonality with the British Army's AS-90. Their proposal called Third generation Maritime Fire support (TMF) could have encouraged joint munitions development and extended its range by up to 50%. BAES were awarded a £4M research contract for TMF in 2007 and this much more powerful gun might have been in RN service by around 2014, had the project not been axed in the 2010 SDSR.

At the time of writing, the Mk 8 Mod 1 soldiers on as main gun equipping the 18 escorts remaining in the RN. It has matured into a reliable, all-rounder with good accuracy and a combat record stretching from the Falklands 1982 to Libya 2011. Unfortunately, its calibre is a dead-end and does not benefit from wider advanced munition developments, while NATO is standardising on 5-inch for its medium calibre naval guns. As far back as the 2000s the RN was flirting with dispensing with Mk 8 for the Type 45s but for budgetary reasons ended up making do with refurbished guns removed from decommissioned Type 42s. Mk 8 manufacture ceased long ago and buying modern weapons available from open production lines was the only viable solution for both the Type 26 and Type 31.

Design of the ‘Global Combat Ship’ began in 2010, the last major iteration of the design that eventually became the Type 26. The competition for a gun that would equip the frigate, known as the Maritime Indirect Fires System (MIFS), was launched in 2012. (‘Indirect’ because medium calibre shells are normally fired a ballistic arc, not directly in a straight line.) It was no surprise when in July 2016 BAES won the £183M contract to supply the Mk 45 for the first three Type 26 frigates. The deal also included a training system, the gun fire control system, ammunition and an option to equip the second batch of 5 frigates. The Mk 45 is manufactured by BAES’ US division at its plant in Louisville, Kentucky but there will be involvement from UK sites in integration, ammunition qualification and safety case assessment. Work to integrate the gun with the new combat management system, Artisan radar and Sea Eagle FCEO system is likely to be a significant part of the cost which will not have to be repeated for the second batch of ships.

When the MIFS contract was made public, British tabloid journalism reached a new level of hilarious incompetence, as the Daily Star newspaper published a piece claiming the MoD had "blown £183 million on a 5-inch gun which is the length of a toothbrush".

The Mk 45 is timeline roughly equivalent to the British Mk 8, originally designed in the 1960s with the 54-calibre Mod 0 entering US Navy service in 1971. The Mod 1 variant arrived in 1980 with selectable munition capability from up to six types, an electronic fuze setter and better metallurgy doubled the barrel life. The Mod 2, with various minor improvements to system controls and ammunition handling subsystems, is still in service on older US Navy cruisers and some export customers. Mod 4 development was begun in the mid-1990s specifically to support Extended Range Guided Munitions to increase range and lethality. The mount was considerably strengthened to accommodate the higher firing energy and the barrel was lengthened to make a 62-calibre weapon with an increased recoil stroke. An Ammunition Recognition System was added together with a new control system. Mod 4 was formally certified during trials aboard USS Winston S Churchill in July 2000. There are now around 240 Mk 45 mounts in service with 11 nations (including 150 Mod 4), the RN becoming the 12th customer.

The Mk 45 is a mostly automated weapon, with 20 ready-use rounds held in the loader drum immediately below the gun. However, in sustained firing operations, the gun needs a six-person crew: a gun captain, a panel operator, and four ammunition loaders working in the magazine manually placing rounds into the hoist. The Type 26 will have a fully automated ammunition handling system (AHS) fitted in the magazine, capable of sustained fire while operated by just one sailor (more details below). Mk 45 propellant charges and shells are handled separately (unlike the single piece ammunition for the Mk 8). This complicates logistics but allows propellants to be interchangeable and is more flexible for future developments.

The Mk 45 has similar performance to the Mk 8 (Mk 8 figures in brackets) although being a slightly heavier weapon, it elevates more slowly at 20º (38º) per second and trains at 30º (42º) per second. This reflects the original design aspiration for some anti-aircraft capability for the Mk 8 while the Mk 45 has always been primarily an anti-surface and naval gunfire support weapon. Mk 45 has a better elevation range of between -15 / +65º (-10 / +55º). Using standard ammunition it has a lower rate of fire 16 – 20 (20 – 26) rounds per minute and fires 31 kg HE shells (21 kg) containing 3.2 kg (3 kg) of explosive to a maximum range of around 36.6 km (27.5km). The standard ammunition types available for the Mk 45 include: High Explosive, Point Detonating Fuze (HE-PD), High Explosive, Variable Time Fuze (HE-VT), High Explosive, Controlled Variable Time Fuze (HE-CVT) and Illumination/star shell.

The Mk 45 above-deck mount weights 22.6 tonnes, with the whole system totalling 60 tonnes without ammunition including below-deck equipment and AHS. The 20-shell drum loader allows separate loading of ammunition to include multiple fuze configurations and specialised propelling charges for extended-length ammunition types. The ammunition and firing sequences can be remotely controlled from the operations room without operator intervention in the gun bay. The Mk 45 has built-in test and self-diagnosis systems to aid maintenance and remote-controlled, power-operated misfire ejection capabilities. A shipboard trial of the Mod 4 firing over 2,500 rounds continuously at maximum firing rate resulted in only three stoppages during the entire test. Overall Mk 45 has demonstrated exceptional reliability in service and is a highly mature system.

BAES has developed the AHS for Type 26 which helps reduce crew numbers. As well as being a safer method of rapidly moving munitions, the system will easily pay for itself over its lifetime in reduced personnel costs. The AHS will feature in the Australian frigates and is on offer to other Mk 45 customers. It can be fitted to existing ships via the gun barbette without the need to cut the hull open. The AHS can supply 6 rounds per minute to the loader drum using the single shuttle system or 10 rounds per minute for the dual shuttle system. The AHS has a maximum capacity of 192 rounds but more can be embarked for bulk stowage in a standard magazine and the AHS can be manually refilled between engagements. The total magazine capacity of the Type 26 is not public but as an indicator, the Type 45 destroyer can embark up to 800 4.5-inch rounds while a US Arleigh Burke-class destroyer can carry 680 5-inch rounds.

With the Mk 45 the RN is buying into a well-supported product ecosystem that benefits from ongoing incremental improvements and a wide customer base. It will also make logistical support easier, giving greater interoperability with US Navy in particular. Ukraine has struggled to support the wide variety of battlefield weapon standards supplied by its allies, this again underlines the importance of commonality if the UK was ever called to fight in a sustained action with NATO partners. The Mk 45 (and 57mm Mk 3) are in service with the UK's most important ally and stocks are likely to be available from the US Navy's solid stores support ships, offering wider resupply options.

Although slightly larger, more robust and a heavier hitter, out of the box, the Mk 45 does not differ dramatically from the RN's existing medium calibre gun but new ammunition developments offer ways to considerably extend its reach and accuracy. In a separate article, we will consider the US Navy's battle to develop extended range and guided munitions for the Mk 45 and the options for the RN when purchasing advanced ammunition types to maximise the potential of the weapon.