The Daewoo assault rifles are the standard issue rifles for the South Korean military and police forces. The K1/K1A short carbines were developed first, the full sized K2 assault rifle was developed later. The K1A is the upgraded version of the K1 carbine (developed as a submachine gun to replace the M3 "Grease Gun" for the South Korean military). The K1A is considered a submachine gun by the South Korean military, despite the fact that it fires an intermediate cartridge (5.56x45mm NATO/.223 Remington) like the full sized assault rifle.
K1/K1A Carbine - telescoping wire stock, short barrel, 1 in 12 rifle twist
K2 Rifle - Folding full sized stock, 16" barrel, 1 in 7.3 rifle twist
While some people regard the K1 as just a shorter 'carbine' version of the K2, they are somewhat different internally. The K1 (which was made first) uses a gas impingement system like the AR15/M16 rifles. The K2 full sized rifle has a gas piston system, just like the AK-47 rifles. Most parts (including the firing pin) are not interchangeable except the bottom stock. Also, Daewoo S&T has recently released a K2 Carbine version along with K3 Para version along with the K12, a 7.62x51mm machine gun to replace the M60.