In the 1870s and 1880s, compressed air was the up and coming form of reliable power proven in mining and tunneling. This flexibility, combined with the problem of how to deliver a new explosive dynamite projectile safely, led the US Army to develop the compressed air cannon.
Preliminary models of compressed air guns were the Reynolds 4-inch bore/420 psig, and 8-inch bore/800 psig models, also known as New Dynamite. Further design and testing resulted in the Model 1890 compressed air cannon that could fire a 15-inch, 1000 pound projectile over 3 miles. The cannon weighed 38 tons and operated on 1000 psig compressed air. Firing air was stored in a 10-ton, 680 cubic foot reservoir. The backup system reservoir was a 20-ton, 670 cubic foot, 2000 psig system. After each round, the firing system pressure would fall about 120 psig and be brought back to 1000 psig instantly by the main air system.
The main air system was fed by a 120-hp steam-driven, reciprocating, in-line horizontal air compressor. Two compressor pistons and one steam piston were mounted on a common shaft. It took one hour to fill the main 670 cubic foot, 2000 psig air system. The air compressor weighed 7-1/2 tons and the steam boiler weighed 9 tons. This equipment (all but the cannon itself), including piping and valves, required a 35 x 80 foot structure for mounting or housing. With machinery this complex, it did not take much neglect to render useless.
With the increase in safety, ease of use, and reliability of the conventional cannon, the compressed air cannon technology was removed from US Army service; without ever firing a hostile round. It would be interesting to know what became of the compressed air dynamite and air cannons and all their machinery. There was never more than brief mentions in Coast Artillery Corp training manuals and it is supposed that the Army disposed of them.
Excerpts and images sourced from Compressed Air Magazine, December 1969, by Konrad F. Scheier, Jr, published by Ingersoll-Rand.