USMC 7-inch Naval Gun Mk.2

As soon as the United States formally entered World War I, plans for an expeditionary force were put into action, but to the United States Marine Corps' chagrin they discovered that they were not to be included in the force. Inter-service rivalry dictated that the American presence in France was to be a US Army affair-with no role envisaged for the Marines. Not surprisingly the Marines made a considerable fuss to the extent that they were eventually told that they could go to France, but only by travelling aboard the US Navy vessels escorting the troopships across the Atlantic. After a no-doubt cramped and uncomfortable crossing the 5th Regiment of the US Marines arrived in France on the 27th of June, rather expecting that they would be immediately committed into combat. The Marines found however, to their great disappointment, that they had been assigned to rear area duties-acting as guards, military police, couriers and garrison troops. As more Marine units arrived senior Marine Corps officers began pressing for permission to form an entire Marine Division to be deployed on front line service.

Unfortunately there lay one major problem to be overcome –in order to become a field Division they would need to include an artillery element within the Divisional structure, and the only Marine artillery formation available (the 10th Marines) was still in the United States. The 10th Marines were equipped with American 3- inch field guns dating from 1902, which although sound and effective pieces, fired ammunition that did not correspond with French standards, and the French 75mm in particular. In 1917 American industry was not yet in a position to produce ordnance of any kind in quantity. This meant that despite the US Army and Marines having American field pieces already in service, there was no industrial infrastructure established to back it up with sufficient guns and ammunition in the quantities that would be required to conduct warfare on a major scale. Thus the US Army in France had to accept French 75mm and 155mm pieces to become seriously operational, and as the Marines in France would be dependent on the US Army for virtually all their supplies this meant that they could not make use of their existing 3-inch guns. In effect with no Marine artillery component there could be no Marine Division. Not to be defeated the Marines approached the US Army and formally requested an assignment of 75mm guns. The army equally formally acquiesced and assigned twenty-four 75mm guns but since all such guns were already earmarked for Army use the chances that the Marines would actually get these guns were very remote indeed. They had to look elsewhere.

They answer was provided by the US Navy which already had plans to convert 14- inch naval pieces into railway guns (some of which saw action in France before the war ended). The attention of the Marine Corps was attracted to a sizeable stockpile of unemployed 7-inch naval guns removed during a modification programme carried out on old Connecticut class pre-dreadnaughts1. The 7inch guns had conventional L/45 barrels mounted on simple pedestals and fired a 74.8kg projectile. The mountings limited the maximum range to just over 15,000 metres, but it was quickly realised that with a higher elevation field mounting this could be increased to 22,000 metres which would be very useful on the French battlefields. They seemed to be just what the Marine gunners needed for employment in France.

A request was made to the Naval Gun Factory in Washington DC to design a field mounting for the 7-inch barrels. It was not an easy task for the guns themselves weighed no less than 13,018 kg apiece which meant that an extremely hefty field carriage would be required to withstand the stresses of firing. With an estimated all-up weight of no less than 38 tons such a load precluded the use of a conventional wheeled carriage (for even with artillery wheels almost two metres in diameter the footprint weight would still be far too much for cross country travel), and thus when the Navy designers commenced their work on 15th March 1918 the use of a tracked carriage was virtually enforced on them. The tracked carriage eventually designed ensured a ground pressure less than half that of a horses hoof which was more than adequate for employment on a ground battlefield2.

Design work was completed on 15 May 1918 and a contract to produce 20 mountings was awarded to Baldwin Locomotive Works at Philadelphia three days later. The contract called for delivery by 18 October 1918. The Baldwin works stuck to their contract and on the appointed date duly delivered the first two carriages to the Washington Navy Yard where the barrels stood ready for use. The mountings and barrels were placed on barges and rowed down the Potomac to Indian head, Maryland, where the Marine gunners were eagerly awaiting their arrival.

The gunners of the 10th Marines3 had already commenced preparation with the array of assorted equipment that would be needed to operate their new guns, including training in the use of the 120hp Holt caterpillar towing tractors, White reconnaissance cars, ammunition trucks, signals gear and all manner of other equipment Once the carriages arrived they were promptly towed away (without waiting for the barrels to be fitted) for instant field trials to demonstrate that the tracks could withstand all manner of use and could travel wherever the tractors could drag them.

The very next day the gun barrels were mounted onto their carriages and proof firing began using of 69.4kg projectiles. The anticipated range of just over 21,900 metres was duly attained and the carriages demonstrated extreme steadiness to the point of requiring no re-laying between shots. Observers from the US Army were on hand to witness the trials and were so impressed that on their recommendation the Army ordered a further 36 carriages for their own use.

But by then it was already too late. The Armistice ending hostilities was signed before the guns could even be loaded aboard their transport vessels at the Philadelphia Navy Yard. In fact the 18 carriages delivered (the final two were cancelled by the end of the war and the army received only 20 mountings out of their order for 36 before cancellation, and none appear to have received their allotted barrels) remained stockpiled at the Philadelphia Navy Yard for some years and were never handed back to the Marines. At least one gun was still there in 1926, but by then the rest had been scrapped. The Marines were eventually supplied with their previously ordered 75mm French field pieces plus a number of 155mm GPF guns. Many of these were still in use when WW2 began.

During the early days of WW2 some 7-inch guns, still on their original naval pedestal mountings, were once again dragged out of warehouses and manned by Marine gun crews as emergency defence weapons around various home-based US Navy installations, but by 1945 it seemed that none were left4. That is until a 7-inch gun still on its tracked mounting materialised at the Naval Surface Weapons Centre at Dahlgren, Virginia. For some years it served as a gate guardian before its historical significance was realised and it was moved to its present location at the US Marine Corps museum at Quantico, Virginia.

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