Taiwanese military power has long been supported by the United States and the island nation received and operated the ubiquitous M113 Armored Personnel Carrier (APC) of 1960 in the hundreds. In an effort to decrease reliance on foreign goods and upgrade it aging line of M113 vehicles, the Taiwanese Army undertook a local program to produce a new generation of Infantry Fighting Vehicle (IFV) using the M113 APC as a starting point. Design work began in the 1970s resulting in formal adoption of the "CM-21 AIFV" (Armored Infantry Fighting Vehicle) in 1978. Much of the lines, form and function of the American design remained intact though there proved enough local changes to the M113 concept to make it essentially a "new" vehicle of Taiwanese origin.
IFVs combine the benefits of an APC with the firepower of a light tank system. In this way, the IFV can transport a combat-ready infantry squad under armored protection, disembark the units and then proceed to provide fire support and protection to the squad through machine guns, cannons and anti-tank missiles. The Taiwanese Army has essentially configured the M113 APC for the IFV role to serve its troop transport requirement.
The CM-21 retained the same internal configuration as the M113 before it with the driver seated at the front-left hull and powerpack to his right. This opened the middle and rear sections of the hull for the passenger compartment. There was a standard operating crew of two to include the driver and the vehicle commander/machine gunner. To this was added seating for up to eight passengers in the aft compartment. The commander was seated just aft of the driver with a provided cupola complete with armored hatch and vision blocks. The forward hull sported a slightly sloped glacis plate consistent with the M113 series while the hull sides are vertical. The rear of the vehicle was squared off and home to a large, rectangular powered door which lowered as a ramp to allow for passenger entry/exit. Hull construction was of all-welded aluminum for protection against small arms fire and shell splinters. This was then improved by the addition of bolt-on armor sections along the front sides and rear of the hull with foam set between the base and added armor layers. The vehicle was fully sealed and therefore amphibious, propelled through the water by the motion of its own tracks. Prior to water entry, the crew engaged bilge pumps and erected a trim vane. Night vision was afforded to the standard operating crew positions though an NBC (Nuclear, Biological, Chemical) protection suite did not prove standard.
Power for the vehicle was served through a British-originated Perkins TV8-640 series diesel engine outputting 215 horsepower. The engine was then mated to an indigenously engineered transmission system while exhausting through venting found along the hull roof, allowing for entry into deep bodies of water. The running gear consisted of five double-tired road wheels to a track side with the drive sprocket at front and the track idler at rear. The vehicle hull was supported through a standard torsion bar suspension system that provided relative comfort for cross country travel. Skirting protected the upper track regions and side hulls to a certain extent.
As an armored fighting vehicle, the CM-21 was given a single 12.7mm M2 Browning heavy machine gun suitable for countering the threats posed by infantry, light armored vehicles and low-flying aircraft. For added defense, the passengers could engage nearby targets through one of five firing ports - one located at the rear hull facing and two to each hull side.
"CM-21" represented the designation of original production vehicles. These were followed by the improved "CM-21A1" with revised mechanics. The "CM-21A2"became a more modern variant incorporating a much improved protection suite. The CM-21 chassis went on to serve as other battlefield roles including Command & Control (with added navigation and communications equipment), Missile Carrier (CM-25), Flamethrower, Battlefield Ambulance, Cannon Carrier, Multiple Launch Rocket System (MLRS) and Mortar Carrier (CM-23) - when outfitted with applicable equipment.
Some 250 to 300 CM-21 vehicles have been produced to date (2013). The CM-21 is expected to be replaced in full by the newer CM-32 "Clouded Leopard" 8x8 wheeled vehicle series based on the preceding CM-31 family line.