For as long as there were military threats from the sea and cannons to defend the land, coastal artillery has been used in many different caliber sizes. Such shore-based artillery were used to shell attacking ships as well as invading amphibious forces. It was such that global military powers felt one piece of shore-based artillery was equal to three guns of the same caliber on ships at sea. The shore based platforms could be hidden behind earthworks or encased within thick walls, keeping them out of sight from the attacking forces and generating a certain level of surprise when utilized. The Empire of Japan constructed the largest naval gun at 18.1 inches (459.74mm) and used these on the famous Yamato-class battleships.
The United States - with two long-running shores to defend - were not lost on the concept of large coastal guns. One of the largest caliber guns to be made in the United States became the M1895 16" (410mm) naval gun constructed specifically for coastal defense - only one was completed by 1914 and this example served at the Panama Canal Zone until 1943. By the time of World War 2, the U.S. Army still required additional large-caliber artillery pieces to help protect its major ports and cities along the coast and ordered additional guns in the 16" size to be forged. Due to global military restrictions imposed by the 1922 Washington Naval Treaty after World War 1, the American Navy was required to cancel the South Dakota-class battleships and the Lexington-class battlecruisers. The new Model 1919 16 inch (406mm) /50 caliber Mark II and Mark III rifled gun barrels built for these two capital classes then became available and 20 of the guns were reassigned to the US Army for their coastal defense needs.
The M1919 guns were massive in presence, measuring some 66.6 feet long and weighing up to 340,000 lbs (170 tons) each. The production process was to wrap steel wire around an inner tube of iron, the steel wire being square and 1 inch on each side. The square wire was kept taught as the iron tube turned in a constant motion. The wire added additional layers around the breech due to the explosion effects of the required powder when firing. When the correct number of layers of wire had been applied, steel hoops were fitted over the wire, then fired, causing the hoops to shrink and merge together into and onto the 1 inch wire (the length and weight of the gun barrel made normal forging impossible). The caliber of the barrel was determined by the ratio of the bore - or 16 inches to the length of the barrel. So one would multiply the caliber (50) times the diameter (16 inches) to equal 800 inches (66.6 feet). The inside of the barrels were right-hand rifled which forced the projectile to rotate clockwise. This "rifling" - called lands and grooves - generated more inherent distance and accuracy for the shell than any smoothbore cannon would have.
The open rear end of the cannon was the "breech" and used to access the firing chamber by loading fresh projectiles and allowing firing to take place with relatively safety to the gunnery crew. Collectively with all applicable components this unit was known as a "breechblock". Comparatively in a standard infantry rifle, the bolt mechanism acted as the "breechblock", just on a smaller scale. The breechblock for the 16 inch gun was called the "Welin breech" which consisted of a single motion screw allowing for fast uninterrupted thread sealing. Used by most Allied heavy naval and field guns of the time, compressed air was used as the primary method to operate the breech. The part of the breech that prevented the hot propellant gasses to escape when firing was the "Debange Obturator" mechanism for each 16 inch shell was not inserted within an all-encompassing brass jacket with the propellant inside that could not escape the jacket. The shell was rammed into the breech and powder (in silk bags) was seated behind the shell. When the powder was ignited, the Debange steel mushroom head was forced against a series of gaskets, preventing escaping of gases out the breech end of the barrel. This gas was instead forced out of the muzzle end of the barrel, adding to the muzzle's energy.
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.
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