The Nexter M811 is an automatic, externally powered, single- or dual-fed cannon firing NATO standard 25 mm ammunition (25 × 137), designed by Nexter Systems (previously Giat Industries). Its intended use is in an air-defence or direct-fire role, mounted on either naval or land platforms, replacing existing 20 mm cannon where applicable. The M811 was first shown in June 1983.
The turret installation was also provisionally selected for installation on the French Army’s Vehicule Blindé de Combat d’Infanterie (VBCI) 8 × 8 Infantry Fighting Vehicle (IFV). In service with Singapore (Dragarturrets on AMX-1 OP Marine) and Turkey (515 guns in Dragar turret for installation on locally built AlFV. Of these, 60 have been supplied by Giat, with remainder being built in Turkey by MKEK. Of the 515 turrets, 67 have been supplied by Giat and the remainder built under licence in Turkey).
The 25 mm Model 811 is an externally powered weapon utilising a cam arrangement to time and drive the internal mechanism and it fires standard 25 x 137 mm ammunition. Ammunition feed is dual and the rate of fire can be selected between the low one (125 rds/min) and high one (400 rds/min). Modes of fire, which can be selected using the electronic controls fitted to the gun are single shot, limited bursts or unlimited bursts. It is possible to start up, operate and service the weapon without firing ammunition. The recoil load is 1,500 daN which makes it suitable for mounting on armoured or unarmoured vehicles. The user can select electric (24 V) or hydraulic drive.
According to Nexter, the accuracy of the 25 mm Model 811 is such that all rounds will hit a 1.5 m diametertarget at a range of 1,500 m. Terminal effect of the 25 mm APDS-T round is equivalent at 1,500 m to that of a 20 mm round at a range of 1,000 m. The explosive mass of the 25 mm HE round is three times that of a 20 x 139 mm round. Current natures available from Nexter Munitions includes the following; High Explosive Incendiary Tracer (HEI-T), Target Practice (TP), Target Practice Tracer (TP-T), Armour-Piercing Discarding-Sabot Tracer (APDS-T) and Armour-Piercing Fin-Stabilised Discarding-Sabot Tracer (APFSDS-T). According to Nexter Systems, the accuracy of the Model 811 25 mm is such that all rounds fired will hit a 1.5 m diameter target at a range of 1,500 m.