Oerlikon KBA

The Oerlikon KBA is a 25 mm (25×137mm) autocannon, developed as a close range multipurpose weapon in the mid-1970s for the mechanized battlefield, originally made by Oerlikon-Bührle (now Rheinmetall AG). It is a positively locked breech, gas-operated cannon with a rotating bolt head and a dual-belt selective feed system taking a 25 mm cartridge. The nominal rate of fire in burst mode is 600 rounds per minute but it can be adjusted electronically and reduced from single shot to selectable range between 175 to 200 rounds per minute.[1]

Oerlikon KBA 25 mm
Oerlikon KBA 25mm Automatic Cannon.png
Oerlikon KBA 25mm Automatic Cannon
Place of originSwitzerland
Service history
In serviceMid 1970s – present
Used bySee operators
Production history
ManufacturerRheinmetall AG
No. built5,000+
Mass112 kg (247 lb)
Length2,806 mm (110.5 in)
Barrel length2,173 mm (85.6 in)
Width263 mm (10.4 in)
Height283 mm (11.1 in)

ShellNATO 25×137mm
Caliber25 mm
Rate of fireSingle Shot;
Rapid Single Shot: 175-200 RPM;
Burst: 600 RPM
Muzzle velocity1,100 m/s (3,600 ft/s)
1,400 m/s (4,600 ft/s)
Effective firing range3,020 m (9,910 ft)
Maximum firing range5,850 m (19,190 ft)
Feed systemDual Feed

Due to its firepower, its range of ammunition and its "Instant Ammunition Selection Device" (IASD), which allows the gunner to easily switch between armor-piercing and high-explosive rounds, the KBA cannon can engage lightly armoured vehicles, infantry, anti-tank positions, helicopters, combat aircraft and ships.


The Oerlikon KBA 25 mm is a fully automatic cannon based on the proven gas-operation principle with a rotating bolt head similar to the Mauser M 98 or M16 and double belt feed for the ammunition.

The KBA offers a wide range of firing modes: single shot, programmable rapid single shot with a rate of fire of up to 175 rds/min, and full automatic fire at 650 rds/min. The cannon functions, such as cocking and firing, are electrically actuated by a remote control unit or manually in auxiliary mode by means of a hand crank and a trigger pedal.

The Oerlikon KBA 25mm cannon has been designed for integration in various types of mounts, small size and low weight offering various integration possibilities such as:

  • Human-operated or remote controlled turrets on IFVs and APCs
  • Air defence gun mounts
  • Naval mounts[2]
  • Helicopter mounts

The various types of available ammunition combined with the unique Instant Ammunition Selection Device and selectable rates of fire support any type of operational use.


At the turn of 1964-65, the United States started the ambitious Bushmaster project started as an offshoot of the US Army's MICV-65 program that was attempting to introduce a new infantry fighting vehicle to replace their existing M113 armored personnel carriers, the Bushmaster project aimed to create small-caliber cannon for the US Army.

The Bushmaster project were intended to meet the requirements for the armament of infantry fighting vehicles (IFV) of the 80's and 90's:

  • Ammunition performance: 25 mm armour steel, 60° (NATO) angle of impact, 1000m range, corresponding to the armour of a well-armoured infantry fighting vehicle;
  • Instant ammunition selection: for engagement of different targets;
  • Selectable firing mode: Accurate single-shot, bursts with a rate of fire of more than 550 rds/min for engagement of aircraft;
  • Compact structure: with low weight for installation in gun turrets of APC's;
  • Simple to operate and service: in the hands of infantry.

At the early stage of American program, one of the companies involved in the development of automatic guns of the Bushmaster program was TRW Inc. (Thompson Ramo Wooldridge Inc.) who entrusted with the development of a 25mm weapon.[3]

The TRW new project was under the leadership of engineer Eugene Stoner, the same author of the famous M16, AR-10 e AR-18, he lead the development of a 25 mm automatic cannon under the internal designation of "TRW model 6425" developed around the experimental 25x137 mm cartridge.

TRW Model 6425 Automatic Cannon

TRW's requirement for the 25mm project where that the gun had to be fully automatic and actively locked, be operated by gas and with rotating bolt, use a dual-belt selective feed system to be able to switch quickly and easily between different type of ammunition.[4]

In parallel the Oerlikon-Bührle assumed responsibility for developing the new ammunition 25x137mm and the interior ballistics of the TRW 6425.[5]

The first prototype was produced in 22 months and began test firing in November 1965 from an Ml 14 vehicle, in December the prototype was fired from an Austrian Armored Personnel Carrier. An early version was tested by a number of countries including Great Britain and France.

At the beginning of 1967, technical tests and firing trials were carried out with two TRW-6425[5] prototype cannons followed by the first demonstrations for a NATO country.

The early configuration was tested several times at Aberdeen Proving Ground, included was a Military Potential Test from March 1968 to March 1970.

Before the U.S. tests were completed, due to the Vietnam War situation the US Army stopped momentary the new IFV project and at the end of 1969 TRW ceased work on the TRW 6425 cannon. In the same year the company Philco-Ford Aeronutronic Division, interested on the TRW project, began work on the weapon when TRW sold the rights of the gun project to them.[6][7][8]

At least six TRW-6425 automatic cannons were built.[7]

When the US Army project started again, the PFB-25 was selected as one of the self powered gun for the U.S. Army Vehicle Rapid Fire Weapons System (Bushmaster), hence the name PFB-25 which stands for Philco-Ford Bushmaster 25mm.[9]

Since then, Philco-Ford has further developed their version, the PFB-25,[9] in the same period Oerlikon started the project "KBA" series which is similar to the 25mm cannon TRW-6425.[7]

Oerlikon KBA 25mm Part Description

In the Oerlikon project, which received the designation KBA (where "K" is kanone; "B" is a 25 mm caliber, "A" is a design model in a given caliber), several principles were combined in order to refine the project.

In the trials, however, the American prototypes PFB-25 displayed a number of basic functional deficiencies during the tests. This persuaded the Oerlikon to undertake their own development work to effect system modifications, which then resulted in the required functional reliability and enabled the trials to be completed successfully in 1970. When the first prototype cannons became available, suitable gun turrets had also to be provided.

The original American design of TRW 6425 where strongly reworked, perhaps only the originally laid down cartridge of 25x137 mm and the method of blocking the chamber by turning the bolt, which was a novelty for the development of Oerlikon, remained from it, earlier systems had sliding bolts with locking lugs. Developed by Eugene Stoner, the classic TRW-6425 cannon automatic gas valve drive has also undergone global changes.[3]

Example of Oerlikon KBA installed on Italian VBM Freccia (IFV) wheeled in use by the Italian Army.

The complete system, cannon, hand-driven turret and ammunition underwent detailed firing trials between 1969 and 1971.

The Oerlikon gives huge development efforts were devoted to improve functional reliability, durability and firing precision of the gun, and in 1971 sufficient progress had been made for the weapon system to fulfill the strict specifications laid down, and to be delivered to the Netherlands in a huge number of cannons.

On 1977, due to internal decision, the US Army selected the Hughes M242 (externally-powered weapon) from Hughes Helicopters Ordnance Division for the new IFV Vehicle who took definitely the name of Bushmaster.[10]

Within the framework of the product support service Oerlikon improves the product and adapts it regularly to the latest requirements. An important step forward was made in 1982/83 when the ammunition penetration performance range of the 25 mm APDS-T (sub-caliber) round was increased 150% from 1000 to 2500 m.

The refined project KBA from Oerlikon, such as high rate of fire, reliability, ammunition performance, good safety record, dual belt feeder with first-round response, no external power requirement and simple maintenance lead to a considerably increasing interest in the Oerlikon KBA 25 mm cannon in years coming.


A wide range of ammunition has been developed for this weapon specifically developed to engage and defeat both ground and air targets.

KBA 25mm on Dutch YPR-765 in Afghanistan

The ammunition complies with all handling and operational safety requirements according to MIL-STD’s, and was subjected to intensive trials by NATO member countries prior to its introduction and standardization as NATO 25mmx137 ammunition.

The current 25x137mm ammunition family consists in different combat (air - ground) and training rounds types as follow:

  • APFSDS-T: Armour-Piercing Fin Stabilized Discarding Sabot with tracer, for use against armoured ground targets;
  • APDS-T: Armour-Piercing Discarding Sabot with tracer, for use against armoured ground targets;
  • FAPDS-T: Frangible Armour-Piercing Discarding Sabot with tracer, for use against air, ground and urban targets;
  • SAPHEI-T: Semi-Armour-Piercing High Explosive Incendiary with tracer, for use against well protected targets;
  • PELE: Penetrator with Enhanced Lateral Effect, for use against armoured ground targets without explosive charge;[11]
  • PELE-PEN: Penetrator with Enhanced Lateral Effect with Penetrator, for use against armoured ground targets without explosive charge;[11]
  • HEIAP: High Explosive Incendiary and Armor-Piercing, for use against armoured ground targets;
  • HEI-T: High Explosive Incendiary with tracer, for use against lightly protected targets;
  • HE-T: High Explosive with tracer, for use against lightly protected targets;
  • MP-T: Multipurpose with tracer, designed to defeat a broad range of targets from soft skinned to armored target and building constructions;[12]
  • TPDS-T: Target Practice Discarding Sabot with tracer, a short range trainer for the above sub-calibre types;
  • TP-T: Target Practice with tracer, used for training.

Mounting & Weapon StationEdit

OTO Melara 25/80 with Oerlikon KBA 25mm (manned configuration).

Here listed the most noticeable Weapon Station and their characteristics under production for the KBA Autocannon:

VALHALLA TurretsEdit

The company VALHALLA Turrets has developed RCWS weapon systems called Valhalla NIMROD 250 designed mainly for IFV, 4x4 vehicles, Tanks and Light Armoured Fighting Vehicle.[13]

The NIMROD 250 turret is designed to mount a 25mm Oerlikon KBA (25x137mm) autocannon paired with high performance electro–optic system (cooled and un-cooled).

In the configuration of the system is present also a co-axial machine gun for additional fire support for the main cannon.


Turkish made Aselsan STOP stabilized weapon station for naval application can be fitted with a Oerlikon KBA.[14]

Turkish made Aselsan NEFER-L remote controlled weapon station is developed primarily against armored land targets.[15]


OTO Melara has developed two-man turret, for armored vehicles called HITFIST. The turrets are designed to mount a 25mm Oerlikon KBA or 30/40mm ATK Mk44 autocannon. The main armament may mount a co-axial machine gun. A variant allows the operator to aim and fire anti-tank missiles. Operators include Italy, Poland and Romania.[16]

OTO Melara has also developed a single OTO 25/80 KBA stabilized weapon station, electric servo-drive assisted for naval application with 252 ready-to-fire rounds. The OTO 25/80 KBA turret is available in the unmanned or manned configuration.[16]


The KBA 25mm Automatic Cannon where installed in many other weapon stations design such: OTO Quadruple Gun Turret (es. SIDAM 25), OTO T25S / T25 Turrets (VCC-Dardo), FMC Turret Type EWS Turret (es. YPR-765), Israeli OWS-25R Turret (es. MLI-84), Type 87 ARV Turret, Oerlikon GBD-ADA Turret, etc

Oerlikon KBA 25mm installed on LEONARDO OTO-Melara 25/80 RCVS


Current operatorsEdit


  1. ^ "Leonardo OTO Melara Oerlikon KBA da 25 x 137 mm". Si Vis Pacem Para Bellum (in Italian). 15 May 2020. Retrieved 2021-12-23.
  2. ^ "Oto-Melara Breda Oerlikon KBA 25/80 mm machine gun system". Seaforces.org. Retrieved 2021-03-19.
  3. ^ a b "Oerlikon KBA(KBB) 25-мм автоматическая пушка". Airwar.ru (in Russian). Retrieved 2021-12-25.
  4. ^ "Automatisch kanon Oerlikon KBA". Nationaal Militair Museum (in Dutch). Retrieved 2021-02-19.
  5. ^ a b Fitchett, Bev (2020-04-19). "Mm Trw Automatic Cannon - Machine Gun V5". Bev Fitchett's Guns. Retrieved 2020-05-11.
  6. ^ Fitchett, Bev (2020-12-18). "Oerlikon Kb 25mm - Machine Gun V5". Bev Fitchett's Guns. Retrieved 2021-12-17.
  7. ^ a b c Chinn, George M. (1987). The Machine Gun, Volume 5. US Navy Bureau of Ordnance. Retrieved 18 December 2021.   This article incorporates text from this source, which is in the public domain.
  8. ^ Fitchett, Bev (2021-03-08). "Trw-6425 Cannon - Machine Gun V5". Bev Fitchett's Guns. Retrieved 2021-12-17.
  9. ^ a b "Philco-Ford PFB-25 (Bushmaster 25mm) Critical Characteristics and Key Technical Requirements" (PDF). National Archives. November 5, 1974.
  10. ^ Fiscal year 1977 authorization for military procurement, research and development, and active duty, selected reserve and civilian personnel strengths hearings before the Committee on Armed Services, United States Senate, Ninety-Fourth Congress, Second session, on S. 2965 ... Washington, D.C. 1976. hdl:2027/mdp.39015074749436.
  11. ^ a b "Medium Calibre Ammunition". Rheinmetall Defence. Retrieved 2022-04-29.
  12. ^ "25mm x 137 Multipurpose Tracer SD". Nammo. Retrieved 2022-04-29.
  13. ^ "Nimrod". Valhalla Turrets. Retrieved 2022-03-17.
  14. ^ "25 mm STOP Remote Controlled Stabilized Naval Gun System". Aselsan. Retrieved 8 July 2021.
  15. ^ "NEFER-L Remote Controlled Weapon Station". Aselsan. Retrieved 2021-12-23.
  16. ^ a b "HITFIST®". Leonardo S.p.A. Retrieved 2021-12-17.
  17. ^ a b "YPR-765 APC - IFV 1975". Tanks-encyclopedia.com. Retrieved 2021-03-03.
  18. ^ a b "Aselsan STOP 25mm Remote Weapon Stations for Pakistan Navy Fleet Tanker Project". Navy Recognition. Retrieved 2017-03-30.
  19. ^ a b c d e f "AIFV 25 Armored Infantry Fighting Vehicle". FTS Belgium.