The K2 supplanted the M16A1 assault rifle as the primary infantry weapon for the South Korean military since its adoption in 1985,[8] though the former remains in service with reservists.

With a modern rifle design and rapid economic growth in the 1970s, South Korea began to build the M16A1 (Colt Model 603K) under license in 1974.

Geopolitical considerations played a factor, as the Nixon Doctrine and Carter administration's use of the U.S. military presence on the Korean peninsula as leverage to force change against South Korea's human rights practices.

[9] Facing the eventual expiration of the license to produce the M16A1, president Park Chung Hee, who strongly believed in self-reliance in national defense, ordered the development of an indigenous standard military firearm.

Prototypes XB-1 through XB-5 were akin to AR-15-series rifles with some exterior changes; designers attempted to use as many M16 components as possible to save time and money, such as the direct gas impingement operation, sights and handguards.

There were several reasons for this: the ROK Army maintained a Cold War-style mentality that favored tanks and artillery against an outdated North Korean threat, leaving less money and urgency to modernize infantry weapons and tactics; the manufacturer had been producing tens of thousands of rifles each year since the 1970s without competition for domestic customers that didn't request upgrades, leaving no motivation to make changes; and various management and ownership changes created internal chaos making it difficult to conduct research and development.

Special forces units had more of a need to upgrade K-series weapons with new optics and accessories, so they turned to private companies to develop add-on rail systems.

[10] The K2 and K1A had become outdated for international markets after 2000; in addition to lack of ability to add accessories, the K1A had become too large, underpowered and un-ergonomic as a personal defense weapon or special operation carbine and the K2 was too long.

S&T Motiv developed the K2A to enhance its domestic appeal, which retained the full-length K2's features (including bayonet lug) and utilized the upgrades of K2C, such as the Picatinny rail on the upper receiver and handguard, as well as an Colt M4-style collapsible stock.

The "C" in the name represented that only the exterior design was modified, without any enhancements made to its performance, in accordance with the Korean Defense Specifications (KDS).

[2] The Republic of Korea Armed Forces originally planned to replace the entire K2 with new S&T Daewoo K11 dual-barrel air-burst weapon.

Despite the shortest handguard ever seen on any assault rifles, the K2C variants have had issues with overheating, and thus most of the K2's around the world are the original K2, with the barrel mostly exposed, unlike the K2C.

When personnel from the South Korean army special command were invited to see the XB-series prototypes, they requested the development of a new submachine gun to quickly replace a series of different weapons in their use.

The barrel used 1:12 inch rifling to fire M193 rounds, as during its development there were no plans to adopt SS109 ammunition in the South Korean army.

The shortened design was adopted as the K1A SMG in 1981 and issued to special forces, commanders, radio operators and others who needed a short SMG-like weapon.

However, due to the K11's extremely high cost and weight for a standard rifle, the armed forces scrapped its original plan and decided to provide 2 K11 per squad in order to increase firepower.