Oerlikon KBA

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 programmable from 100 to 175 rds/min and full automatic fire up to 600 rds/min. The cannon functions, such as cocking and firing, are electrically actuated by a remote control unit or manually operated, 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:

• Manual gun mountings for armoured vehicles and naval vessels.
• Remote Controlled Weapon Stations for armoured vehicles and naval vessels.
• Air defence systems.
• 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 US Army started the ambitious MICV-65 program to replace the M113 armored personnel carrier with a new infantry fighting vehicle. As an offshoot of MICV-65, the Bushmaster project aimed to create a new medium-caliber cannon for the US Army.

The Bushmaster project was intended to meet the armament requirements of future infantry fighting vehicles of the 1980s and 1990s:

• Ammunition performance: penetrate 25mm of steel armour, at a 60° (NATO) angle of impact, at 1000m range, corresponding to the armor of a well-armored 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 APCs.
• Simple to operate and service: in the hands of infantry.

In 1960, the American company TRW (Thomson, Ramo-Wooldridge Inc.) Jet & Ordinance Division, soon to become TRW Inc., developed the experimental 25x137mm gun as part of the Bushmaster project.^[6] The new TRW project was to design an automatic cannon around the experimental 25mm cartridge under the company internal designation of "TRW-6425". The project leader was engineer Eugene Stoner, the designer of the famous ArmaLite AR-10, AR-15, and M16A1 family of assault rifles.^[7]

TRW's requirements for the 25mm project were that the gun had to be fully automatic and actively locked, be operated by gas, have a rotating bolt head and use a dual-belt selective feed system allowing a quick and easy switch between different ammunition types.^[8] In parallel Oerlikon-Bührle assumed responsibility for developing the new 25x137mm ammunition and the interior ballistics of the TRW-6425.^[9]

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^[9] prototype cannons followed by the first demonstrations for a NATO country.

In the meantime the Swiss Oerlikon-Bürle factory obtained the European license for the TRW-6425 from TRW in 1967,^[10] and started the "KBA series" 25mm cannon project based on it.^[11] In the designation KBA, "K" stands for Kanone (gun), "B" indicates 25mm caliber and "A" is the design model in a given caliber. Several principles were combined in order to refine the project.

At least six models of the TRW-6425 automatic cannons were built.^[11] The early configuration was tested several times at Aberdeen Proving Ground, included was a Military Potential Test from March 1968 to March 1969. Before the U.S. tests were completed the US Army paused the new IFV project due to the Vietnam War situation. At the end of 1969 TRW ceased work on the TRW 6425 cannon. In 1970 the Jet and Ordnance Division of TRW Inc. was closed and Stoner, together with Robert Bihun, launched ARES Inc. As ARES Inc. quickly outgrew Stoner's garage, they moved the company into the same buildings previously used by TRW Inc. and hired many of their former employees.^[12]

Following the closure of the TRW Jet and Ordnance Division, the Philco-Ford company's Aeronutronic Division became interested in the TRW-6425 cannon project, bought the rights to the project and began work on the weapon.^[13][11][14]

When the Bushmaster project—full name U.S. Army Vehicle Rapid Fire Weapons System (Bushmaster)—was restarted, the PFB-25 (Philco-Ford Bushmaster 25mm) was selected as one of the self-powered gun candidates.^[15] Since then, Philco-Ford has further developed the PFB-25.^[15]

During the trials, the original American PFB-25 prototypes displayed a number of basic functional deficiencies. This prompted Oerlikon to undertake further development work on the KBA. Oerlikon extensively reworked the original American TRW 6425 design. Perhaps the only remaining elements of the original design in the KBA were the 25x137 mm cartridge and the method of blocking the chamber by turning the bolt (a novelty for Oerlikon development, earlier Oerlikon systems having sliding bolts with locking lugs). Eugene Stoner's classic automatic gas valve drive from the TRW-6425 cannon was also comprehensively changed.^[6] The resulting modifications added functional reliability that allowed the trials to be completed successfully in 1970. When the first prototype KBA cannons became available, suitable gun turrets had also to be provided.

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

Oerlikon devoted huge development efforts to improve the functional reliability, durability and firing precision of the KBA autocannon. In 1971 sufficient progress had been made for the weapon system to fulfill the strict specifications laid down and for large-scale deliveries to the Netherlands to begin.

In 1977, due to an internal decision, the US Army selected the externally-powered Hughes M242 from Hughes Helicopters Ordnance Division as the Bushmaster. The M242 became the autocannon for the Army's new IFV.^[16]

Within the framework of their product support service Oerlikon regularly improves the gun and ammuntion, and adapts them to the latest requirements. An important step forward was made in 1982/83 when the range at which the 25 mm APDS-T (sub-caliber) round achieves its specified performance was increased by 150% from 1000m to 2500m.

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

• HE-PX: High Explosive, Proximity Fuze with controlled fragmentation, for C-UAS application.^[17]
• 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;^[18]
• PELE-PEN: Penetrator with Enhanced Lateral Effect with Penetrator, for use against armoured ground targets without explosive charge;^[18]
• 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;^[19]
• 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.