Gunpowder has been used so long that alternatives are rarely discussed.  The US Army and Navy considered liquid propellants for large guns during the 1990s.  Ideally, two liquids would be used which are inert themselves, but highly explosive when mixed (like Triex and Quadrex). The gunner would turn valves so the desired amount of liquids mix in or near the gun chamber.  This would allow the use of very high explosives for greater range, using a foolproof safety concept. Obviously, the "gunpowder" industry was not thrilled with this idea and it has been dropped.

      The next leap forward in propellants may be compressed air. The US Army used a "dynamite gun" (below), really a pneumatic or compressed-air gun, with an effective range of 900 meters during its 1898 fight in Cuba.  This gun first ignited black powder in a combustion chamber to instantly generate air pressure.  This low velocity gun was of modest success, but was discarded as new cased ammunition proved superior.  

         However, modern gun systems could use powerful commercial air compressors to achieve far greater power.  A powerful diesel compressor could rapidly compress air in the gun chamber.  The US Air Force uses a gas gun to fire projectiles MACH 7 as part of its scramjet research; see  AEDC ScramjetAir is far less hazardous since it is not transported and stored, it is just sucked out of "thin air."  This would cut ammo transport and storage needs in half.  Air is also much cheaper than chemical propellants; its free.  Rate of fire is another advantage since artillery guns can only fire a couple rounds of minute for a sustained periods because heat build-up can damage the barrel, and explosive gases wear out barrels.  Compressed air causes less heat and barrel wear, and no residue, so it would not have to be constantly cleaned or replaced.  Air doesn't produce a muzzle flash either, something that makes today's guns very visible at night.  Finally, released compressed air causes far less noise, so an enemy may have no warning that rounds are be inbound.

      Modern engineers would need to determine how the projectile could be loaded and how long it would take a compressor to generate the necessary pressure, although jack hammers "fire" rapidly. The range could be changed simply by adjusting the air pressure. Since range is based on the ability to compress air and the strength of the barrel, it would be possible to fire a projectile hundreds of miles. To achieve such pressures, highly compressed air may have to be "crushed" within a gun chamber with a hydraulic vice.   

     Boosting range with rocket propulsion is possible if each projectile had a rear chamber with a small hole.  As the air pressurizes in the gun chamber, it automatically pressurizes the air in that chamber.  After the projectile leaves the gun barrel, the compressed air in the rear chamber sprays out to reduce drag and propel the round.  An even more radical step would be to replace the explosive in the common blast/fragment munitions with compressed air.   Extremely inexpensive and safe projectiles would be injected with compressed air just prior to fusing.

      The use of pneumatic guns for warships has already been tried.  A "dynamite gun cruiser" the USS Vesuvius (below) was commissioned in 1890 with three 15-inch pneumatic guns.  These guns were fired during the Spanish American war with mixed results.  The quiet guns surprised the enemy, but they were not mounted on turrets, so aiming was difficult.  It was a crude design with a maximum range of 2000 meters, which was adjusted by changing the air pressure.


      Air cartridges may also be developed for small arms. CO2 cartridges have been used in powerful air guns for years. Perhaps highly compressed air could replace gunpowder in cased small arms ammunition. The advantages are significant, no muzzle flash, and no barrel heating problem for machine guns. The use of compressed air as a propellant is where the Pentagon should devote money for a "Revolution in Military Affairs". 

                                      Carlton Meyer