UK Royal Marines Adopt SIG Sauer MCX

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 reads: “The UK Commando Force has been issued with 1,500 new Sig Sauer MCX rifles for use in the maritime counter-terrorism role.”

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 Spear-LTs while Marines from 40 Commando are seen using the KAC KS-1 L403A1, which was adopted by elements of the UK Commando Force and the new Army Special Operations Brigade made up of the battalions of the Ranger Regiment which was formed in 2021.

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-pattern carbines in service: the new L143A? (MCX), 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 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 Spear-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.

At SHOT Show 2025, SIG Sauer had one of the rifles on display but couldn't offer details.

From the released imagery we can see that the rifle, a Spear-LT, seen at SHOT 2025 matches. The rifle is equipped with a SIG Romeo 8T red dot sight and Juliet 5x magnifier, mounted on a UK-marked mount, as well as a compact SLXC suppressor.

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 (MSO), Maritime Interdiction Operations (MIOps), Joint Personnel Recovery (JPR), Support and Influence Operations (S&I), and Ships Force Protection Teams (SFPT).

42 Commando won't be the only unit to deploy the new rifles. UK Commando Force Operations confirmed on X 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) 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.