The UK’s Royal Marines have confirmed that some units of the UK Commando Force are now equipped with the SIG Sauer MCX. The announcement on social media simply read: “The UK Commando Force has been issued with 1,500 new Sig Sauer MCX rifles for use in the maritime counter-terrorism role.” These are set to be used alongside the new Knights Armament-produced KS-1s which were adopted in 2023 as the L403A1.
The first confirmation that the MCX was in British service came in February, with the publication of a video titled ‘RAID’ showcasing the Royal Marines Commandos’ capabilities. In the video members of 42 Commando are seen using SIG MCX LTs while Marines from 40 Commando are seen using the L403A1, which has been adopted by elements of the UK Commando Force and the new Army Special Operations Brigade, which is made up of the battalions of the Ranger Regiment which was formed in 2021. Check out my earlier article/video looking at the L403A1 here.
In a full statement the Royal Navy, under which the Royal Marines operate, said the procurement was “part of £6m Navy investment” with the new rifles “designed to complement the Commandos’ new general use weapon [the L403A1].”
This means that the UK Commando Force have at least four AR-patterned (in terms of ergonomics and layout) carbines in service: the new MCX variant, the L403A1 (KAC KS-1), and the L119A1/A2 (Colt Canada C8) which is available in a standard configuration with a 15.7 in barrel and in the C8SFW configuration which has a CQB upper receiver with a 10 inch barrel. Additionally, they also deploy the 7.62x51mm AR-10-pattern L129A1, with plans in the works for an A2 chambered in 6.5 Creedmoor.
Lieutenant Colonel Olly Osborne, of the Commando Force Programme team, said: “These rifles reinforce the commitment of the Navy and Defence to our transformation, and the value the Commando Force provides to our national and international security. This is an excellent period of investment in the force and provides great confidence through exceptional task specific modern weaponry.”
The rifle was procured under the auspices of Project Hay, during which the Royal Navy says that Commandos “put the system through strenuous testing during force-on-force exercises and live firing drills… [they were able to] thoroughly field-test systems and provide feedback on their performance. This was instrumental in shaping the final configurations of the fielded MCX.”
A different configuration of the MCX LT was previously part of the Project Hunter trials. The Royal Marines Commandos’ MCX will replace the short C8SFW with trials of a .300BLK upper and associated ammunition said to be ongoing. This will likely be used in conjunction with reduced ricochet, limited penetration ammunition.
At SHOT Show 2025, SIG Sauer had one of the rifles on display but couldn’t offer details at the time.
From the released imagery we can see that the rifle, an MCX LT, seen at SHOT 2025 matches. The rifle has a 12.5in barrel and is equipped with a SIG Romeo 8T red dot sight and Juliet magnifier, mounted on a UK-marked mount, as well as a SLXC compact suppressor.
In addition to the 5.56x45mm chambering the Royal Marines will also field a .300BLK configuration which has a 9in barrel and accessories (including the stock, an SLX762QD suppressor, magazines, rail scales and optics) in black finish while the 5.56x45mm chambered carbines all feature FDE-coloured accessories (as seen above). This system is intended to prevent the mix up of ammunition between the two weapon systems preventing accidents. As with the earlier L403A1 procurement the MCX carbines were procured via UK-based Edgar Brothers.
UK Commando Force is made up of a number of specialist units; 42 Commando, the unit seen equipped with the rifles in the RAID video, specialises in Maritime Security Operations, Maritime Interdiction Operations, Joint Personnel Recovery, Support and Influence Operations, and Ships Force Protection Teams.
42 Commando won’t be the only unit to deploy the new rifles. UK Commando Force Operations confirmed that L403A1 Alternative Weapon System (AWS) is the primary weapon for 40 Commando and 45 Commando, and the Commando Force’s Surveillance and Reconnaissance Squadron (SR). The latest figures from the UK MoD confirm that delivery of 1,620 carbines have been completed. but that the MCX will also equip 47 Commando Raiding Group. Other UK Commando Force elements will retain the Colt Canada C8, with the aim of replacing remaining SA80 series weapons currently in use.
In a recent article Soldier Systems Daily, who has a close relationship with SIG Sauer, noted that the procurement of the Royal Marines’ MCX-pattern carbines had been carried out two years ago with delivery completed in 2024. The Royal Navy’s announcement did not state what the weapons’ designation is but several models of MCX have been in UK service for a number of years, largely within the ecosystem of UK Special Forces. Sources suggest that these MCX are designated the L143A1 and L143A2, it remains to be seen if the new rifles will be designated the L143A3 or be classified as A2s.
Most recently, UK Commando Force shared several photos and a short video of the MCX at the range, with a Royal Marine demonstrating how the weapon can be fired with the stock folded. This is a useful feature for operating in confined spaces during boarding operations.
This article was adapted from a piece originally published at TFB.
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The Armourers Bench 