The K-21 is a replacement for the South Korean K200-series infantry fighting vehicles, formerly designated as K300 or XK21 KNIFV (Korea Next-generation Infantry Fighting Vehicle). The initial production was set for 2008, with the Republic of Korea Army planning to field approximately 466 units. It is designed to effectively defeat other IFVs as heavily armed and armored as the BMP-3. Unlike the infantry transport armored vehicle K200, the K21 infantry fighting vehicle is literally the infantry fighting vehicle (IFV) that introduced the concept of “transport for infantry troops with combat capability”.
The K-21 is lighter comparing with most modern IFVs, as it was designed using composite materials to save weight wherever possible. It features 20% lighter weight and 50% lower price competitiveness than other countries. The K21 IFV has achieved a high localization rate and is expanding the line-up into 105mm turret loaded medium tanks and medium recovery vehicle. It is the top-of-the-line armored fighting vehicle with excellent performance. It is known that front arc provides protection against 30-mm armor-piercing rounds. All-round protection is against 14.5-mm armor-piercing rounds. The K-21 can be also fitted with active protection system, similar to that used on the South Korean K2 Black Panther main battle tank.
The two-man turret on the K21 is armed with an S&T Dynamics K40 40 mm cannon capable of firing APFSDS, high-explosive, smoke and multipurpose munitions, and a 7.62 mm machine gun. This is combined with an advanced fire-control system and gun stabilizer usually found on third-generation main battle tanks that makes the K21, together with the German Puma, able to move and engage the targets with high degree of accuracy at the same time. The 40 mm cannon can fire up to 300 rounds per minute, with a projectile velocity of up to 1,005 m/s (3,300 ft/s). The improved APFSDS rounds fired from it is able to penetrate up to 160–220 mm (6.3–8.7 in) of armor, slightly higher than other APFSDS rounds, due to the self-sharpening process as the round penetrates the armour.
The K21 is equipped with Doosan D2840LXE V-10 diesel engine, equipped with a turbocharger. The vehicle itself is approximately 25.6 tonnes which, combined with the total output of the engine, gives it a power/weight ratio of approximately 29 hp/t. The K21 PIP will feature an improved version of the engine that will give the vehicle an increased power of 840 hp. A newly developed semi-active ISU, or In-arm Suspension Unit, is available for the K21. The same unit is to be used on the K2 Black Panther. Despite having the same ISU used on the K2 Black Panther, the K21 cannot change its posture. The vehicle can travel on both land and water. “Pontoon System” gives more buoyancy to float on water when additional weight is put on to the vehicle.