The primary projectile was Armor Piercing (AP) in nature, weighing 2,100, 2,240 or 2,340 pounds depending on exact projectile being utilized. The powder charges were packed with 110 pounds of nitrocellulose propellant and were encased inside of bags of special silk that burnt, leaving no residue in the barrel. The powder was smokeless with a high burning rate and a normal charge was six bags - or 660 pounds - of gun powder necessary to launch the 16 inch shell. The distance from gun to target determined the amount of bags of powder to be used as well as the elevation of the barrel - as such much training and skill was required in the gun's function. The maximum charge was eight bags of powder - or 832 pounds - for the Army Mk II and Mk III guns. To fire the gun, the lock hammer was tripped by a lanyard or an electric current. The primer cap then ignited the black powder in the primer and fired a flame through the vent in the obturator spindle, igniting the charge of black powder located on the end of the last powder bag - the "main" charge. The shell could then travel some 44,680 yards (40,855m) from the gun.
The next important function of the gun was the recoil of the barrel. As one can imagine, launching of 16 inch shells generated quite a bit of violent force. The required "reverse" action was a mechanism controlled by two pneumatic cylinder recuperators. Inside of the cylinder was air charged to 1,700 psi and an oil-water mix of 60% oil and 40% water. As the gun recoiled, the air psi increased to 3,400.
As can be expected, regular maintenance to prevent corrosion of the guns various systems. Long rams tipped with burlap and soaked in soapy water were used to clean the inside of the barrels while all metal parts were coated with oil to stop the salty seaside air from rusting out parts.
Ultimately, these M1919 guns were placed within concrete casemates and used to deter and protect American cities, harbors and targets of value but none were ever fired in anger for no enemy warships arrived to attack the 48 states, Hawaii or Panama directly. By 1952, the 16-inch guns and their carriages - all but one - had been cut into pieces and sold as scrap metal, much the same fate that greeted many of the expensive wartime naval ships - even some legendary ones. The last Mk III M1 Navy #138, mounted on barbette carriage S/N 1, is on display at the Ordnance Museum at the Aberdeen Proving Grounds in Maryland. While the rest of the museum has since been moved to Fort Lee, Virginia, the MKIII and her barbette remain at Aberdeen due to her excessive weight.