Artillery Evolutions: Counter Battery Fire with the 4.7-inch Gun

As mentioned earlier, when the U.S. expanded the field artillery arm to support American Expeditionary Force (A.E.F.) going to France in 1917, planners saw the need for a medium caliber gun to provide counter-battery fire.   Unlike the other artillery types, the Americans had a weapon on hand to fill this need – the Model 1906 4.7-inch Field Gun.

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Well Restored M1906 4.7-inch Field Gun

The Ordnance Department developed the M1906 4.7-inch Field Gun in the decade before World War I.   The Army had sixty of these guns on hand when the U.S. declared war in 1917.  These were among the few American designed guns to see service in France during the war.

Overall the gun reflected conventional design thoughts.  The gun itself was of built up composition with a jacket extending beyond the breech. The jacket attached to a recoil lug.

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Rear of gun showing recoil lug, rods, and cylinders

The gun tube sat upon a cradle with two cylinders underneath housing the long-recoil, hydro-spring system.

The service manual described the recoil action:

The gun moves to the rear 70 inches on the cradle ways, carrying with it the piston rod, spring rods, and spring-rod yoke and compressing the counter-recoil springs.  As the recoil cylinder remains stationary the oil behind the piston must pass to its forward side.  The energy of the recoil of the gun is absorbed by the resistance which the oil offers to being forced through small openings past the piston and by the resistance of the counter-recoil springs.  The energy stored up by the springs returns the gun to its firing position.  This return movement is eased and regulated by the counter-recoil buffer.  The piston-rod pull and spring resistance are transmitted to the carriage, but owing to its weight and the resistance opposed to the trail spade by the earth the carriage remains stationary.

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Trail spade in "up" or traveling position
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Spade in the "down" position - note maneuvering spikes

The breech was a standard interrupted screw with four flats.  A handle swung from left to right, rotating the block, in one continuous pull.  An extractor ejected the empty casing.

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Partly Open Breechblock

Although the gun could fire out to 11,000 yards at 25° elevation, the carriage restricted elevation to 15° and 7,500 yards with a 60 pound high explosive shell.  Traverse was just under 8°, constraining the arc of fire.  But the sighting system borrowed from the successful setup on the M1903 3-inch gun. The gun fired a common high explosive shell containing 3.36 pounds of TNT.

The shrapnel shell contained 711 half-inch steel balls.

In addition the Army fielded gas projectiles during the war.  All rounds for the 4.7-inch gun were fixed, meaning attached to the brass cartridge case, enabling a relatively high rate of fire.

Like the smaller divisional guns, the 4.7-inch gun’s box-trail carriage used a two wheel limber for movement.  With the limber the gun weighed 9,800 pounds, requiring an eight horse team.  This is one reason the U.S. Army set its eye on mechanical prime movers.

At the start of the war, the Army ordered new production batches of the M1906 in order to fill the anticipated need.  As we have seen with the lighter field guns, the Production Board spread the manufacture of the gun out by components.  Rock Island Arsenal, Studebaker Corporation, and Walter Scott Company produced gun carriages to include the recoil system;  American Car & Foundry Company and Maxwell Motor Company produced the limbers;  Northwestern Gun Company and Watervliet Arsenal produced the guns themselves.  In addition American Car & Foundry Company and Ford Motor Company produced caissons.  All told the Army ordered around 750 complete guns.

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Muzzle markings indicating Watervliet manufacture

A well established product entering mass production – nothing to worry about right?  Well three issues (I won’t say problems) arose which limited the 4.7-inch gun’s use.  First, given the desire to remain compatible with French ammunition stocks, planners suggested re-lining the gun to that nation’s 120mm round.  On its face, this sounded like a simple change of millimeters.  However the French 120mm system dated to the 1880s and was quickly departing that nation’s inventory.  Some historians have cited this issue as causing major delays.  I’ve yet to see documentation proving this was more than a paper project anyway.  The companies listed above were already working on 4.7-inch patterns, and the distraction was minimal in my opinion.

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Front View of M1906

The second issue was also ammunition related.  The 4.7-inch was supposed to fire counter-battery missions against German divisional guns.  The 4.7-inch could counter the standard German 7.7cm FK 96 n.A., which ranged only to 6,000 yards.  But the newer 7.7cm FK16 then arriving at the front had a 10,000 yard range, effectively negating the 4.7-inch as a counter-battery gun.  The solution was to adopt a lighter 45 pound shell for the 4.7-inch, allowing for 8,700 yards at 15°.  Furthermore, the Army standardized the practice of “digging in” the trail to allow the 4.7-inch gun to launch shells to its maximum range of 11,000 yards.  Although that required more preparation by the gun crew.  The ultimate solution was a split trail to allow greater on carriage elevation.  Prototypes just such a mounting were at the test ranges as the war ended.

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M1906 showing solid box trail of the carriage, which limited elevation

The most important issue facing mass production of the gun was the gun tube forgings.  Because of the different diameters between the muzzle and breech, manufacturers had difficulty in the heat treatment of the steel jackets.  With a production bottleneck emerging, the Production Board ordered gun tube jackets produced by Edgewater Steel Company in Pittsburgh.  The jackets went to another company on the other side of Pittsburg for machining.  From there the jackets went back to Edgewater for heat treatment. From there the jacket went to the gun-maker who was assembling the other components.

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M1906 - breech and rear of gun

Sounds inefficient, right?  The eventual solution was a redesigned jacket, separate breech ring attaching to the recoil lugs.  However the redesign was too late for the war effort.  With the production bottleneck, only sixteen new production 4.7-inch guns joined forty-eight pre-war examples in France.

While the board sorted out production issues, the Army turned to alternatives.  From the seacoast artillery came twenty-eight 5-inch and ninety-five 6-inch guns.  The Navy contributed forty-six 6-inch guns of various models.  And the firm of Francis Bannerman & Son (a major military surplus dealer of the era) offered thirty 6-inch guns of 30 calibers.  While working gun tubes, these guns lacked field carriages and required other adaptations before issue to the field.  By mid-1918 the Army had the twenty-eight 5-inch gun outfits weighing some 12 tons, but which could fire a shell nine miles.  A similar adaptation for 6-inch guns weighed 21 tons and ranged ten miles.  None of these outfits were worth shipping to the war zone.

Ultimately the solution for the A.E.F., as with the divisional guns, was foreign supplies.   Among the foreign types supplied to the A.E.F. was the British 60-pdr (5-inch) Field Gun in both Mark I and II variety.  Weighing even more than the American 4.7-inch, this beast needed a Holt Tractor to move around the battlefield.  American corps artillery also received quantities of the French 155mm Grande Puissance Filloux (GPF) mle 1917.  But I will save detailed discussion of that piece for another post.

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60-pdr Mark I

In retrospect, the 4.7-inch gun was another sad story in American procurement.  A sound design with much promise, the 4.7-inch was not adapted for mass production.  But the Ordnance Department certainly heeded this lesson and applied it to inter-war design.  In the next war, the US Army would not rely upon foreign cannons.