During the Vietnam War, considerable numbers of South Korean military personnel were deployed to the country in support of the United States military. The U.S. supplied South Korean troops with M60 machine guns, which were quickly adopted and then manufactured under license by Daewoo Precision Industry (now S&T Motiv). From 1970 to 1990, the M60 was South Korea's universal machine gun, being used by infantry and mounted on vehicles and helicopters. Because the Republic of Korea armed forces was heavily influenced by American military doctrine, when the U.S. Army adopted the M249 squad automatic weapon in the 1980s, the South Korean Army and Marine Corps followed suite and introduced the K3 light machine gun, a "Koreanized" version of the FN Minimi, for squad use. During the 2000s when aging M60s first needed replacement, platoon-level machine guns were replaced by K3s which removed the medium machine gun from infantry, a departure from U.S. doctrine which uses medium machine guns for platoon-level fire support. The M60 remained in use on vehicles and aircraft, but even some Korean-made armored vehicles were armed only with K3s.
Since the K3 was in production while M60 assembly lines had long been closed, it seemed obvious to the ROK military to replace the M60 with it. However, due to the short range and limited power of the 5.56 NATO round, South Korean tanks, armored cars, and helicopters retained their M60 variants firing 7.62 NATO ammunition. Most M60s were still working relatively well and the military did not want to spend money to find a replacement machine gun, choosing to use their budget to focus on more expensive and high-value assets. The search for a new medium machine gun finally gathered momentum in 2006 when the ROK Army began the development of the Korean Utility Helicopter, a domestic medium utility helicopter. The new helicopter created a requirement for new machine guns for them, as both the UH-1H Hueys and the M60s they mounted remained from the Vietnam War. Army leaders initially wanted to buy from foreign vendors, especially the FN Herstal M240H, but others in the Army and S&T Motiv used the opportunity to develop an indigenous 7.62 mm machine gun.
S&T Motiv began development under the name XK12 in July 2010. By the time gun prototypes began to be mounted and tested on KUH helicopter prototypes, they had already fired 300,000 rounds without any serious problems. In 2012, the XK12 was adopted as the K12 light machine gun as the standard armament of the KUH. Currently, the K12 is only in use for the 300 planned helicopters, but there is potential to expand its use. The ROK Army has 2,300 tanks each usually having two M60 guns, and a similar number of other vehicles armed with one M60. Furthermore, U.S. experiences in Iraq and Afghanistan has soldiers desiring medium machine guns to return to infantry outfits. Large orders may later open up export markets.
The K12 is based on the K3's design, layout, and function using a gas piston and rotating bolt. It is fed through a STANAG M13 disintegrating belt link and cannot accept a magazine. The cross-bolt type safety is the same as K3/Minimi, and the receiver is made from steel press with an aluminum alloy feed cover. Although similar in design, the receiver and other important parts are enlarged to accommodate the larger round. The K12 is somewhat heavy for the gun class at 12 kg (26 lb), mainly because it has pistol grip, spade grip, and metal sliding stock all in one gun for the purpose of being quickly converted into a ground-fire machine gun by a dismounted operator; the spade grip can be removed by taking out two pins, removing the grip, and unfolding the stock which is similar in design to the FN Minimi’s Para version. Standard machine gun features are included like a folding (K3-style) bipod, quick change barrel, gas regulator, and (M240H-style) flash suppressor. It also has a folding ring sight for firing on helicopters with a folding ladder type sight for more accurate aiming. The sight is attached on a Mil-Std 1913 rail, which is also on the feed cover and both sides of the handguard. No laser or optical sight has yet been selected for use on the K12, but some kind of electro-optical accessories are expected in the near future.