The Colt Infantry Automatic Rifle is the new automatic weapon for Singapore's army, replacing a local design that has been used for over four decades. As reported by Jane’s, the Singapore’s Ministry of Defence (MINDEF) said the Colt IAR was chosen to replace the Ultimax 100 after extensive trials and evaluations of various models, as part of its force modernisation efforts.

The MINDEF did not disclose any details about the contract or the production of the Colt IAR.

Singapore has a history of making its own weapons, starting with the Colt AR-15 and M-16 rifles in the 1970s and later developing its own designs with the introduction of the ST Engineering Land Systems Ultimax 100 in 1982. The Colt IAR  fires 5.56 mm cartridges and uses a gas-operated system to cycle the action. It has an air-cooled barrel and a magazine-fed mechanism to feed ammunition. It can switch between semi-automatic and fully automatic modes of fire for sustained periods.

The Colt IAR competed against the Heckler & Koch's IAR entry in the US Marine Corps' IAR competition in 2009 and eventually called the M27 IAR. The other alternatives that Singapore considered before selecting the Colt IAR are unknown. ST Engineering may have offered updated versions of the Ultimax 100, such as the Mk.8 version that was displayed since 2012.

The Ultimax 100 is a rifle that has excellent control and a long history of service in Singapore. The design team behind this rifle was under the guidance of American firearms designer L. James Sullivan who designed it with a special mechanism that reduces recoil when shooting in full auto mode. It uses a 30-round STANAG magazines just like the Colt IAR but also can use a 100-round drum magazine and it's considered to be one of the lightest machine guns in the world. In the USMC IAR competition, the Ultimax was also an entry with the Mark 4 variant with the addition of a new fire selector module.

In a video released by the Singapore Army called "Our Singapore Army, A Stronger Army", which highlights what it has done in 2022, a quick segment showed the Colt IAR at 2:58 as the "New Section Automatic Weapon":

The other known user of the Colt IAR is the Mexican Marine Corps.