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The Apache has a McDonnell Douglas M230 30-millimeter Chain Gun, which is a mechanically operated automatic weapon driven by a bicycle-style chain looped around the firing mechanism box. The scheme is simple -- in fact, so simple that in hindsight it is puzzling why it hadn't been invented decades earlier -- as well as lightweight and reliable.

The cannon is supplied with 1,200 rounds of ammunition and has a maximum rate of fire of 650 rounds per second. Its 30 millimeter ammunition is compatible with the British Aden and French DEFA 30 millimeter cannon. The usual ammunition is the M789 High-Explosive Dual Purpose (HEDP) round (see below), which features an armor-piercing hollow charge with a fragmenting case. The HEDP round can penetrate 5 centimeters (2 inches) of rolled steel armor.

The Chain Gun is on a hydraulically-driven swiveling mount between the forward landing gear legs. It can be pointed 11 degrees up, 60 degrees down, and 100 degrees to either side. If hydraulics are lost, the cannon pops to its stowage position, with the barrel forward and up. There is a void in the nose above the cannon into which the weapon collapses in a crash, reducing injury to the crew.

M789 HEDP
High Explosive Dual Purpose

Team: LW30mm
Height (max): 199.75mm
Weight: 350.5g
Number Produced: 3M
Muzzle Velocity (nominal): 800 m/s
Chamber Pressure (typical): 415 MPa
Trace (typical): Available
Penetration (typical): 25mm RHA @ at 500m

The ATK LW30mm HEDP ammunition features a spin-compensated, shaped-charge liner for superior armor defeat plus additional growth potential. Outstanding armor penetration, combined with blast, concussion and fragmentation characteristics, gives the LW30mm ammunition superior multi-role, multi-target capabilities.

Combat proven in Operations Iraqi Freedom, Just Cause and Desert Storm, the LW30mm demonstrates excellent armor penetration at ranges from 150 to 4,000 meters.