20mm Vulcan

     Notes:  The Vulcan, and its upgraded version, the PIVAD, is one of the most common air defense guns in the world, whether in trailer-mounted versions, fixed mountings, naval mountings, and vehicular use.  A modified form is a very common aircraft gun.  The Vulcan is a six-barreled rotary cannon that fires at an extremely rapid rate of fire, projecting a virtual wall of metal at targets.  The standard model has a range-only radar and a generator; the PIVAD adds a new digital optical sight, and a ballistic computer.  A third model, the Basic Vulcan, is designed for export to poorer countries; it deletes the radar, digital sight, and power controls for elevation and traverse. 

25mm M-242 Chain Gun

     Notes:  Also known as the Bushmaster, this autocannon is fitted to the M-2 and M-3 Bradley Fighting Vehicles and the LAV-25, as well as US Navy deck mountings.  It is also employed on MOWAG Piranhas used by the Saudis.  Rounds may be fired on semiautomatic, ROF 2, ROF3, or ROF5.  This weapon fires both US-made and European ammunition.  The mechanism is actuated by a chain drive, hence the name. It is noteworthy that before Operation Iraqi Freedom, the US Army was heavily considering replacing the Bradley’s 25mm M-242 with a heavier-caliber autocannon; however, the 25mm M-242 has outperformed expectations and its replacement is no longer being considered.

25mm Objective Crew-Served Weapon

     Notes:  This weapon was designed to partially replace the Mark 19, ASP, and M-2HB.  The OCSWs rounds, like the OICWs grenade launcher rounds, can be set to airburst over a target’s heads or strike the target directly.  The OCSW fires a special 25mm round with a computerized proximity fuse, either HE or HEDP.  The OSCW is fired from a lightweight tripod developed especially for this weapon, or it may be fired from a NHT mount.  The OCSW uses a computerized laser sight, a slightly improved version of the IR imaging sight on the OICW. The OCSW is fed from special cassettes of 22 or 74 rounds. 

     Twilight 2000 Notes: The Objective Crew-Served Weapon (OCSW) was rushed into service several years ahead of its target date, however, few were available by the Twilight War.

     Merc 2000 Notes: Budget cuts largely ended deployment of this weapon.

30mm ASP

     Notes:  The ASP-30 (Automatic, Self-Powered) is a gas-operated version of the 30mm ChainGun designed as an infantry support weapon.  It fits on an NHT or any other mount that is equivalent to an NHT.  It is fed from a 50-round belt.  Recoil is manageable when on a tripod or vehicle mount. 

30mm Mk 44 Bushmaster II

     Notes: This weapon is an upgraded M-242 Chain Gun, and retains 70% commonality of parts with that weapon.  The Bushmaster II can use the same ammunition as the GAU-8, and can also fire 30mm Rarden and KCB ammunition.  It is used on US Navy deck mounts, and on the Swedish CV-30, and on some versions of the AAAV. 

35mm Bushmaster III

     Notes:  This is a belt-fed autocannon which is just beginning to be mounted on AFVs; antiaircraft and naval use is still more common.  The Norwegian variant of the CV-9040, for example, uses the Bushmaster III. 70% of the parts of this weapon are compatible with the Bushmaster I and II.  It fires ammunition identical to that of the 35mm Oerlikon autocannon, though some new warhead types were developed along with the Bushmaster III.  The Bushmaster III has been designed to, after the replacement of the barrel and some monor parts, to be able to fire 50mm Supershot ammunition, effectively becoming a 50mm autocannon.  As of yet, this has not been done on an operational basis, but the concept has been thoroughly tested and is ready for deployment upon request.

     Twilight 2000 Notes: This weapon has been mounted some versions of the M-2 and M-3 Bradley.

75mm ARES XM-274

     Notes: Initial development of this heavy autocannon began in 1973 as part of the US Army’s HSTV-L and HIMAG programs; the development was sponsored by the US DoD’s ARRADCOM Large Caliber Weapons Laboratory, and though the design work was done by ARES personnel, most of the work was done at this facility and ARRADCOM provided partial funding.  The XM-274 was originally going to be used in both a light armored gun system as well as in a self-propelled antiaircraft gun system, but the HSTV-L and HIMAG programs came to naught.  However, in 1981, ARES received renewed interest in the XM-274 from the Army, as possible armament for its RDF/LT program vehicle, the supposed replacement for the M-551 Sheridan at the time.  In conjunction with AAI, a light armored gun system which could be airdropped was designed, using a low-profile turret and a special feed system for the gun.  However, this program too eventually came to naught.  ARES and MOWAG got together and produced a test version of the Piranha II armed with this gun, but no one seemed interested.  Test vehicles with the XM-274 as armament were also made on a LAV-25 chassis, again with no takers. Eventually, the gun was shelved, though ARES still retains the design in their inventory and is willing to put it into production if someone is interested.

     The XM-274 is a heavy autocannon firing revolutionary (for the time) case-telescoped ammunition.  In vehicular applications, the gun is fed from a 36-round carousel in the floor of the vehicle under the low-profile turret, though ARES is willing to consider and has proposed other feed designs.  The CTA ammunition reduces its volume and its weight, as well as making feed more reliable.  The XM-274’s design called electrical priming of the rounds and a recoil/hydropneumatic system for operation.  Spent cases are ejected upwards and outside of the vehicle.  The XM-274 is designed to function optimally firing in short bursts of 1-5 rounds, with a cyclic rate of one round per second.  The barrel is fairly long at L/75.48 (5.661 meters), giving it good accuracy and power despite the relatively small caliber of its rounds.

     At the time of the cancellation of ARES’s entry in the RDF/LT program, ARES was working on a 90mm version of the XM-274, but the rate of research was slow as ARES concentrated on the 75mm version, and only two such prototypes were made.

     Twilight 2000 Notes: In the Twilight 2000 timeline, this autocannon is mounted on the LAV-75 light armored gun system.