The U.S. Naval 7-inch Track-propelled Gun Mk.2 1918
by Tim Rigsby
 

 

The 7-inch naval gun is mounted on an unorthodox carriage for field use, not wheeled but tracked and that by itself will mark it as among the first pieces of heavy artillery to make use of a caterpillar track – long before, say, the Soviet WW2 203mm tracked artillery piece, and contemporary with the French 194mm St Chamond SP Gun.

The Background

As soon as the united states formally entered the war, plans for an expeditionary force were put into action. But the Marines found out they were not included in the upcoming forces being sent overseas. It seems that the American presence in France was to be predominantly the Army. Finally after the marines received their shipping orders, they would have to travel across the ocean on cramped an uncomfortable U.S. Navy vessels escorting other troopships across the Atlantic.

After the 5th Regiment of the U.S. Marine Corps arrived in France, on June 27, 1917, they were ready for combat.  They were soon disappointed, instead being placed in the front line they found themselves assigned to all manner of miscellaneous jobs. And even though these jobs were essential to the upkeep of an army in the field, it was not what they came across the ocean to do. The marines found themselves acting as guards, military police, couriers and garrison troops instead of being ''the first to fight'', as they had expected. It was a bit of a blow to marine pride.  It made sense in military terms, as it allowed the U.S. Army to keep the 1^st  infantry division intact as a combat force.

Despite the initial setbacks, the Marines were not too disheartened. The arrival of the 5^th Regiment and other Marine units swelled their numbers in France.  Combat honours such Belleau Wood were soon to come.  The prospect of an entire marine division in action in France seemed very likely.  The formation of a marine division entailed the creation of a marine artillery force to support it.  While there were plenty of marine foot soldiers, artillery was another matter.  The marines has long possessed their own integral artillery element in the form of first field artillery battalion.  By 1917, this had been expanded into the mobile artillery force.  During January 1918, it was reorganized into the 10^th Marine Regiment.

In 1917, U.S. Marine corps artillery units were equipped with American 3-inch field guns dating from 1902.  These guns were sound and effective pieces, but their ammunition was not up to French standards, especially the French 75mm.  Since the Marines in France would be dependent on the U.S. Army for virtually all of their supplies, they did not take their 3-inch guns to France.  That meant no marine artillery in France.  Determined not to be outdone, the marines approached the U.S. Army and formally requested an assignment of 75mm guns. The army drew up an acquisition and assigned to the marines no less than 24-75mm guns. The U.S. Army later stated that no 75mm guns were available and indeed they were not.

American industry in 1917 was not yet in a position to produce ordnance in any kind of quantity. This meant that despite the fact that the U.S. Army and Marines were having American field pieces already in service, there was not any industrial infrastructure established to back them up and produce them (and their ammunition) in the numbers the Great War demanded.  The U.S. Army had to accept French 75mm and 155mm pieces to be fully operational until America’s industrial might could supply them with American ordnance. Regretfully, the Marines getting their 24 guns was very unlikely, so they had to start looking elsewhere.

 

The Gun

The U.S. Navy already had plans to convert 14-inch naval pieces to railway guns which saw action in France. At the same time the Marines had their eyes on a large stockpile of 7-inch guns left over from a modification to the old Connecticut class of pre-dreadnoughts. The 7-inch guns had conventional 1/45 barrels mounted on simple pedestals and fired a 74.8kg projectile. Their mountings limited the maximum range to just over 15,000 meters. A higher elevation field mounting opened the prospect of an increase to about 22,000 meters, which of course would be very useful on the French battlefields. The guns seemed to be just what the marine gunners were looking for as their “ticket to France”.

 

The marines requested the naval gun factory in Washington D.C. to design a field mounting for the 7-inch barrels. This was soon recognized as being easier said than done.  In turn it also meant a large field carriage that could withstand the recoil and other forces involved, resulting in an carriage with an estimated weight of 32 tons.  This precluded the use of a conventional wheeled carriage, for even with artillery wheels almost 2 meters in diameter, the footprint weight would still be far too much for cross country travel.  So, when the navy designers commenced their work on March 15, 1918, the use of a tracked carriage was virtually forced on them.  The tracks eventually used produced a ground pressure less than half that of a horse’s hoof, which was more than adequate for the task. 

 

The design work also involved the introduction of a new counter recoil mechanism for use at the maximum elevation angle of plus 40 degrees.  Overall, the carriage design was orthodox and unadventurous (apart from the tracks) of Holt design.  With the accent on ease of production, huge steel joists prevailed and a wheeled towing limber was constructed entirely from heavy steel components.  Design work was completed on May 15, 1918 and a contract to produce 20 mountings was awarded to the Baldwin locomotive works in Philadelphia, Pennsylvania on June 18, 1918. 

The contract called for the delivery of 2 mountings by October 18, 1918.  Upholding the contract, the Baldwin locomotive works delivered their first two carriages on October 18 to the Washington naval yard, where their barrels stood ready waiting for them.  The mountings and barrels were placed on barges and towed down the Potomac river to Indian Head, Maryland, where the Marine gunners were eagerly awaiting their arrival.

The 10^th regiment had by then been expanded into two battalions that included the 1^st, 9^th, 13^th, 85^th, 91^st and 92^nd companies.  For some time they had been training to receive their new guns with other equipment, such as the White reconnaissance vehicles, ammunition trucks, signalling gear, and all manner of other similar equipment, including the 120-hp Holt caterpillar tractor.  Two of the Holts greeted the barges as they arrived and promptly towed the new carriages away for instant field trials to demonstrate that the tracks could withstand all manner of use and could travel where ever the tractors could tow them.  The next day, the guns were mounted on their new carriages and test firing began.  The anticipated range of just over 21,900 meters was duly attained.  The carriages demonstrated extreme steadiness to the point of requiring no re-laying between shots!  Observers from the U.S. 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.

The Armistice arrived before the guns could even be loaded onto their transport vessels at the Philadelphia naval yard.  Eighteen guns had been delivered, the last two were cancelled by the end of the war.  The Army had only received 20 mountings out of the original order of 36.  The Marines were eventually issued with their previously requested 75mm French field pieces, plus a number of 155mm GPF guns.

The 7-inch story seemed to be over.  Some guns still on their original naval pedestal mountings were once more dragged out and manned by the marines during the early stages of World War 2.  They were used as emergency  defence weapons around various U.S. Navy installations. It has been rumoured that some 7-inch guns were passed to Brazil, but this still requires confirmation.  By 1945, it seemed that no 7-inch gun was left, that is until one still on it’s tracked mounting materialized at the Naval Surface Weapons Centre at Dahlgren, Virginia.  For some years, it served as a gate guardian before it’s historical importance was finally realized.  It was moved to it’s present day location at Quantico.

The Quantico Gun Today