A board of inquiry in South Korea found that design defects were the cause of two new K21s (Infantry Fighting Vehicle) sinking while engaged in amphibious operations. The K21 entered service in November, 2009, and one sank the next month, and another last July. The cause of the sinkings was attributed to a lack of buoyancy (common with amphibious armored vehicles), a malfunctioning wave plate (another common failing) and a technical problem with the drain pump. The fix involves increasing the height of the wave plate, careful distribution of weight before going into the water and a redesign of the drain pump.
The two sinkings resulted in one soldier drowned, and a lot of nervous K21 users. In general, such sinkings are not unusual, as attempts to make armor vehicles float, while theoretically possible, never work out all that well in practice. The South Koreans initially believed that the problem was just some minor flaw in the vehicle design, but the history of amphibious armored vehicles indicates the major problem is often designer hubris. That may still be the case, but South Korean engineers are confident they have found the problems. Troops will be more careful when they take these vehicles into the water. South Korea originally planned to buy about a thousand K21s, but that has since been cut to 450.
The K21 IFV (Infantry Fighting Vehicle) is a 26 ton vehicle, similar to the 33 ton U.S. M-2. The K-21 has a crew of three and carries nine infantry in the back. The two man turret carries a 40mm autocannon, with 200 rounds, as well as two ATGM (Anti-Tank Guided Missile) launchers and a coaxial (with the 40mm) 7.62mm machine-gun. Top speed is 70 kilometers an hour.
The big difference between the K21 and M-2 is weight, and that is mainly because the chassis of the K-21 is made of fiberglass. This material is as strong as metal, but much lighter. This led the South Korean designers to believe that they had a safe amphibious armored vehicle. Armor protection of the two vehicles is equal. The K21 armor can stop 14.5mm bullets and most artillery fragments (it is vulnerable to 152mm shells exploding closer than 10 meters, but at that distance, the blast effect would do serious damage).
The 40mm autocannon fires up to 300 rounds per minute, at speeds of 1,000 meters per second (3,100 fps). The anti-tank round can penetrate up to 220mm of armor. The 40mm can also fire a multipurpose shell, where the gunner can select proximity (exploding close to a target), air burst (exploding above the ground), as well as armor-piercing or fragmentation effect.
Like the M-2, the K21 carries an extensive load of electronics, for fire control, navigation and diagnostics. The K21 designers learned from other recent IFV designs and attempted to improve on their best characteristics. The K21 costs less than $3 million each. But the K21 is not expected to have much more protection from roadside bombs than the M-2. This may prove to be an intractable problem, given that the MRAP gets its protection from its V shaped underside, specific design elements that cannot be incorporated in a vehicle like the K21.