K21 is a South Korean tracked infantry fighting vehicle (IFV) in service with the Republic of Korea Army.

K21 IFV was formerly designated K300 or XK21 KNIFV (Korea Next-generation Infantry Fighting Vehicle), and was developed to replace the older South Korean K200-series infantry fighting vehicles and armoured personnel carriers.

K21 infantry fighting vehicle was designed between 1999 and 2008 by the South Korean Agency for Defense Development.

Serial production started in 2008 at Hanwha Defense (former Daewoo Heavy Industries) facilities.

With a price per unit of $3.2 million, a total of 400 K21 infantry fighting vehicles have been built so far in three lots.

A total of 240 K21 lot number one (Lot 1) and lot number two (Lot 2) were manufactured between November, 2009 and April, 2013, followed by 160 Lot 3 units in 2016.

With a mass of 25.6 t (25.2 long tons; 28.2 short tons), K21 IFV has a length of 6.9 m (23 ft), a width of 3.4 m (11 ft), and a height of 2.6 m (8.5 ft).

It has a crew of three (3) persons and can carry up to nine (9) passengers.

Regarding the protection, K21 IFV chasis is made of 2519 aluminium alloy.

The armor consists of layers of S2 glass fiber and reinforced Al2O3 ceramic armor.

K21 offers all around protection against 14.5×114 mm API projectiles as well as 20 mm FSP.

The K21 frontal armour is resistant to 30 mm APDS rounds fired from a 2A72 autocannon, the standard gun on the BMP-3 IFV turrets.

The roof armour is resistant to 155 mm artillery shell fragments.

The K21 PIP variant is equiped with soft-kill and hard-kill anti-missile defence systems, and ERA and NERA modules.

The main armament of the K21 infantry fighting vehicle is a S&T Dynamics K40 40 mm autocannon with 240 rounds.

Two Hyungung ATGM launchers are planned to be added.

As secondary armament K21 has 7.62 mm M60 general-purpose machine gun.

The South Korean K21 IFV is powered by a 740 hp Doosan D2840LXE diesel engine, while the K21 PIP variant has a more powerful 840 hp engine.

K21 has a power-to-weight ratio of 29.2 hp/tonne, uses an in-arm suspension unit and has an operational range of 500 km (310 mi).

K21 can reach a maximum speed of 70 km/h (43 mph) on road and 40 km/h (25 mph) off-road.

It is an amphibious capable infantry fighting vehicle and it can move on water with a speed of 7 km/h (4.3 mph; 3.8 kn).