US Navy Mk 4 14 inch/50 caliber gun - Largest Allied gun of World War I

The US Navy Mk 4 14 inch/50 caliber guns were used on the rail ways to defeat the Germans in the closing months of World War I.
"Upon its entry into the war, the US chose its largest and longest-ranged available naval gun to fill the gap - the 14"/50 caliber Mk 4 gun with a muzzle velocity of 2800 feet per second. The new 16-inch gun would have been preferable, but it was not yet available in numbers; spare 14-inch guns kept for the active fleet were used instead.
Baldwin Locomotive Works delivered five trains for the United States Navy during April and May 1918. Each train transported and supported a 14"/50 caliber Mk 4 gun mounted on a rail carriage with four 6-wheel bogies.
There was some doubt as to whether the Flanders coast and French Channel ports were now safe Allied ports following the German Spring offensive successes in March and April 1918 which brought those areas within German artillery and attack range. The guns were therefore diverted from the British zone in the north to further south, to the port of St. Nazaire, to avoid the risk of having such valuable assets captured or destroyed.
Each battery composed of a locomotive, gun car, ammunition cars, supporting equipment cars, and accommodation cars for the crew was under the command of a United States Navy lieutenant, and under overall command of Rear Admiral Charles Peshall Plunkett. After delivery by ship, these trains were assembled in St. Nazaire in August.\
Before a gun arrived at a firing position, a curved length of track was laid at a position calculated suitable for firing at a specific target, and a pit 9 feet deep involving the removal of 103 cubic yards of earth was dug between the rails into which the gun recoiled 44 inches. Supports were also embedded in this pit connected to the gun mounting, to transmit remaining recoil energy directly to the ground and avoid placing excessive vertical strain on the gun car (and, through it, the track) and prevent it from moving backwards. In fact, by late 1918 the French had already constructed many such curved spurs (épis) for their own guns and hence the US guns were often able to re-use these^.
The gun car was positioned over the pit, the wheels were locked and the platform was locked into position with gun mount and car's weight shifted from the trucks (bogies) directly to the ground by jacks and lifting screws. The gun could elevate up to 43° which gave it a maximum range of 42,000 yards (23.8 miles/38.4 km), and could be traversed 2.5° left and right of center. Any greater change of direction required the gun to be moved forward or backward along its curved track and a new recoil pit dug. The gun used the standard naval gun mounting and recoil system, with the addition of a pneumatic system to assist the runout springs to return the gun to firing position after recoil at the higher maximum elevation of 43° compared to maximum 30° in naval use^.
A major disadvantage of the Mark I mount was that the weight was distributed forward, placing weight on the leading axles that was above the normally allowable weight for French railways and also caused axle bearings to overheat at any speed over 5 - 10 mph. The armored enclosed gun house lacked ventilation and caused condensation to form which promoted rusting. The necessity to excavate a recoil pit was also not acceptable as a longterm solution of recoil control. Hence Mark I, while functioning as designed, was seen as only a compromise measure necessitated by wartime time constraints.
The guns served to support General Pershing's army offensive in the Meuse-Argonne sector of the Western Front in France. They operated as single-gun batteries designated Battery 1 - Battery 5. Battery 2 commanded by Lieutenant (JG) E D Duckett, US Navy, had the distinction of being the first all-US gun (crew, gun and ammunition) to fire in action on the Western Front. On 6 September 1918 they fired from the forest of Compiegne at the important German railway center of Tergnier in support of an Allied attack.
The guns were used to target key infrastructure deep behind the German lines such as railway junctions and other lines of communication and concentration, typically only opening fire after an Allied attack had begun to avoid giving the Germans any warning of Allied intentions.
They fired a total of 782 shells on 25 separate active days on the Western Front at ranges between 27 and 36 kilometers. This equated to an average of 156 rounds per gun, which was approximately half the 300 rounds expected life of these guns before they would need refurbishment. The guns were only fired for specific strategic purposes to conserve barrel life, with smaller guns being used whenever possible. Hence on many days they remained inactive or were being moved.
The last shot was fired by Battery 4 at 10:57:30 am on 11 November 1918, timed to land just before the scheduled Armistice at 11 am.
One of these guns is on display outside the U.S. Navy Museum at the Washington Navy Yard."