CM-21 - a Taiwanese indigenous design based on the M113, with many improvements and design changes to meet ROCA requirements. The size, shape and performance of the CM-21 is almost identical to the M113.

The Armoured Infantry Fighting Vehicle (AIFV) was developed by the Republic of China Armoured Fighting Vehicle Development Centre in the 1970s and the first prototype was completed in 1979. The Armoured Infantry Fighting Vehicle was manufactured by the Republic of China Fighting Machines Command which was responsible for final assembly and testing. There were approximately 40 companies involved in supplying major components for the AIFV, including the Taiwan Machinery Manufacturing Corporation (suspension and complete power plant) and the Taiwan Aluminium Corporation (hull and tracks). This is understood to have the local designation CM-21 while the variant with the Raytheon Systems Company TOW ATGW is referred to as CM-25. This is the standard TOW ATGW system, not the M901 originally developed to meet the operational requirements of the US Army.

Most sources state that about 250 of the CM-21 series vehicles were built. It was never offered on the export market.

The AIFV is based on the US BAE Systems, Ground Systems Division (previously United Defense) M113 APC which has been in service in Taiwan for many years but incorporates features of the M113A2, M113A3 and the private venture BAE Systems, Ground Systems Division AIFV.

The layout of the AIFV is similar to the M113 series with the driver at the front left, diesel power pack compartment to his right and the troop compartment at the hull rear.

The hull is of all-welded aluminium armour construction with an additional layer of laminate steel armour bolted to the hull front, sides and rear. Closed cell polyurethane foam is used to fill the space between the two layers of armour and this gives increased buoyancy for amphibious operations.

The driver has a single-piece hatch cover that opens to the rear and day periscopes for observation. The power pack compartment has a firefighting system. The vehicle is powered by a British Perkins TV8.640 diesel developing about 215 bhp, coupled to a transmission developed by the Institute of Industrial Technology in Taiwan, and is similar to the M113A1. The air inlet, air outlet louvres and exhaust pipe outlet are in the roof of the vehicle.

The commander sits to the rear of the driver and has a cupola, which can be traversed through a full 360°. This is provided with a single-piece hatch cover, day periscopes for all-round observation, a .50 (12.7 mm) M2 HB machine gun and a shield that gives front and side protection against small arms fire. Either side of the shield is a bank of three electrically operated grenade dischargers firing forwards.

The troop compartment is at the rear of the vehicle and the infantry enter and leave via a power-operated ramp in the hull rear. This has an emergency door in the left side. There are five firing ports, each with a day periscope or a vision block provided, two in each side of the hull and one at the rear. These allow the infantry to use its 5.56 mm weapons from within the vehicle in safety. It is believed that between six and eight infantrymen are carried plus the crew of two (commander/gunner and driver). In addition, there is a hatch in the troop compartment roof.

The suspension is of the torsion bar type and consists either side of five rubber-tyred road wheels with the drive sprocket at the front and idler at the rear. There are no track-return rollers. The upper part of the suspension of the vehicle is covered by a rubber skirt.

The electrical system is similar to that of the M113. Standard equipment includes bilge pumps and night vision equipment. The AIFV is fully amphibious being propelled in the water by its tracks. Before entering the water, bilge pumps are switched on and a trim vane erected at the front of the hull. An NBC system is not installed at present.

An armoured fuel tank, similar to that offered by the now BAE Systems, Ground Systems Division for the M113A2, is fitted either side of the hull ramp at the rear.

Physical and performance characteristics of the AIFV are similar to those of the M113A2.

More recently another version of the basic CM-21 has been revealed called the CM-21A1. This is believed to have a number of automotive improvements. The latest CM-21A2 has a new and enhanced armour package.

The following variants are believed to be in service or under development:

• Mortar carrier (81 mm, 107 mm and 120 mm). The 81 mm mortar carrier is believed to be designated the CM-23A1

• Command post (command, communications and fire direction)

• AIFV with 20 mm or 30 mm cannon

• AIFV with Kung Feng IV 126 mm multiple rocket system; details of this version are given in a separate entry.

• AIFV with Raytheon System Company TOW ATGW system. Maximum range of the TOW anti-tank missile is 3,750 m. This is also used by Taiwan in the standard tripod launched infantry version.

• AIFV with Kuen Wu ATGW. In many respects this is very similar to the Russian Kolomna KBM 9K11 Malyutka (NATO AT-3 'Sagger') ATGW system.

• Others could include fire support vehicle, reconnaissance vehicle, flame-thrower, cargo carrier and ambulance.

Production complete. In service only with the Taiwanese Army. It is believed that total production of this vehicle amounted to between 200 and 300 vehicles. To this must be added over 650 US-supplied M113 series vehicles and numerous specialised models. In the future the ROC fleet of full tracked APCs is to be supplemented by a new wheeled vehicle called the CM-32. This 8 × 8 vehicle is currently at the pre-production phase.