4.7-inch L/22.5 Army Howitzer on M1917 Railway Mount
(Panama Canal Zone During World War I)
The 4.7-inch howitzer on its Model 1908 field carriage was adapted to a railway mount (M1917) for use in the Panama Canal Zone during World War I. The 4.7-inch Howitzer on Railway Mount Model 1917 was a Model 1913 howitzer mounted on a simple railway carriage, and was used as a coastal defense weapon at Panama after the American entry into the First World War.
Deployment: Panama Canal Zone During World War I
During World War I, the United States deployed 4.7-inch howitzers on M1917 railway mounts to the Panama Canal Zone as part of the canal’s defense system. These were medium-caliber artillery pieces (4.7 inches, or 120 mm) that had been adapted for mobility by mounting them on railcars. The decision to send railway artillery to Panama came after the U.S. entry into WWI (April 1917), amid fears that German naval raiders or other threats could target the vital Panama Canal.
The purpose of this deployment was to provide a mobile coast defense capability – guns that could be quickly moved by rail to cover either the Atlantic or Pacific approaches of the canal as needed. At the time, many of the permanent heavy gun emplacements in Panama were still under construction, so this rail-mounted howitzer was a stopgap measure to bolster canal defenses. Four 4.7in Howitzer railway mounts were almost complete when the United States entered the First World War in 1917. They were completed and sent to Panama to help guard the Canal Zone.
Technical Specifications – 4.7-inch Howitzer
The 4.7-inch howitzer itself was a U.S. Army artillery piece dating to the 1910s. It fired a 4.7 inch (120 mm) diameter shell, and could use either a 60 lb (27 kg) heavy shell or a lighter ~45 lb (20 kg) shell. On its original field carriage, the gun had a hydro-spring recoil system and a box trail. It was capable of about 15° elevation and 8° traverse on the field mount. The muzzle velocity was around 1,700 ft/s (520 m/s), giving a maximum range of approximately 7,000–8,700 yards (6.5 to 8 km) depending on the shell weight.
The 4.7in Howitzer Model 1913 was a wire wound gun, with an interrupted thread breech block and a mechanical firing mechanism. It was normally used on a static pivot mounting as a coastal defence gun, but this railway mount was produced to provide a more mobile version. The howitzer was carried on a pedestal, with the recoil mechanism built into the top carriage, along with the elevating and traversing mechanisms. The 4.7in Howitzer used a hydro-spring recoil system that was combined into a single cylinder. The cylinder was fixed to the barrel, and recoiled with the gun, while the piston was fixed to the mount and remained stationary as the gun was fired. The counter-recoil spring was attached to the cylinder, and the head of the cylinder acted as the piston for the spring. The system allowed for 12in of recoil.
This howitzer was one of the few American-designed medium artillery pieces available when the US entered WWI, and about 60 had been built and issued to the Army by early 1917. (It was initially developed as the 4.7-inch Gun M1906 for field use, and a variant was the 4.7-inch Howitzer Model 1913 on fixed pedestal mount.) The howitzer fired high-explosive shells suitable for both high-angle fire (to strike targets behind cover) and direct fire against ships or land targets. In the Canal Zone, these shells would have been effective against smaller vessels, shore targets, or any attempted enemy landings – though they were too light to sink a heavy warship, they could still do damage and had a valuable deterrent effect.
The M1917 Railway Mount – Design and Features
To turn the 4.7-inch howitzer into a mobile coast defense unit, the U.S. Ordnance Department in 1917 designed a specialized railway mounting (Model 1917) for it. This involved placing the howitzer onto a railcar platform that could be moved on standard-gauge tracks. Technical details of the M1917 railway mount are scant in published sources, but it essentially consisted of a flatcar reinforced to handle the gun’s recoil, with a central pedestal or pivot on which the 4.7-inch howitzer was mounted.
The railway car had bogies (railroad wheel trucks) at each end for movement on the Panama Canal Zone’s rail lines. For firing, the car would be braked and likely jacked or blocked in place to absorb recoil. Contemporary railway artillery designs often incorporated mechanisms for limited traverse and elevation: the 4.7-inch on M1917 mount probably had a similar elevation range to the field version (or possibly improved if a pedestal was used) and a small on-carriage traverse. For wider horizontal aiming (azimuth), the crew could position the railcar on curved track sections or pre-surveyed firing spur tracks to train the gun left or right. (Larger U.S. railway guns of the era featured outriggers and rotating mounts for all-around fire, but a 4.7″ howitzer mount would have been simpler.)
Deployment to the Panama Canal Zone
When and why were these weapons deployed to Panama? Records indicate that the 4.7-inch howitzers on M1917 railway mounts were sent to the Canal Zone around 1918. The U.S. War Department recognized that the newly opened Panama Canal was strategically critical and had to be defended against enemy attack during WWI. Early in the war, the Canal’s fixed defenses were still incomplete – the Army was in the process of installing large seacoast guns and mortar batteries at forts on each end of the canal. To reinforce the zone in the interim, the Army deployed some mobile artillery. The 4.7-inch railway howitzers were part of this emergency armament. According to ordnance documents, a small number of these mounts were produced and allocated to Panama’s Harbor Defenses
In all, four 4.7″ railway howitzers were sent to Panama, probably so that two could protect the Atlantic entrance (around Fort Randolph/Fort De Lesseps area near Colón) and two at the Pacific entrance (around Fort Grant/Fort Amador near Balboa). This deployment would have allowed coverage of both ocean approaches and the ability to rapidly redeploy the guns along the tracks. The Panama Canal Zone had an extensive rail network (originally the Panama Railroad) that not only ran the length of the canal but also had spur lines to various fortifications and critical points, which made it ideal for this use.
The strategic rationale for these guns was to guard against several potential threats: a raid by an enemy cruiser or armed merchant ship attempting to shell the locks or shipping; a landing of a sabotage team or troops on either coast; or even an uprising or riot (though that was less a concern than foreign attack). By having mobile 4.7-inch artillery, the Canal Zone commanders gained flexibility – they could reposition the guns based on intelligence of enemy movements or to participate in drills at different locations. In essence, the railway howitzers added a layer of defense in between the heavy fixed guns and the lighter field artillery that were also available.
The mount’s designation “M1917” indicates it was finalized in 1917. It was likely built by a U.S. manufacturer (such as the Baldwin Locomotive Works, which built many WWI-era rail mounts) and shipped to Panama by late 1917 or 1918. The complete unit – gun plus rail carriage – probably weighed on the order of a few dozen tons. This was light enough to be transported on the existing Panama Canal Railway that ran the width of the isthmus.
In fact, a key advantage of rail-mobile artillery in Panama was that it could be “shifted from one ocean to the other in less than a day” via the trans-isthmian railroad if needed. (This concept was proven even more dramatically in the 1920s–1930s when 14-inch railway guns were stationed in Panama under a similar principle.)
The weapon had to be loaded at -10 degrees of elevation, and had a screw elevation system that could reach up to +40 degrees, using hand wheels mounted on both sides of the carriage. The gun was mounted on a pedestal that could be traversed using another hand wheel, and could traverse through 360 degrees.
4.7-inch L/22.5 Howitzer on Railway Mount Model 1917
Caliber
4.7 Inch
Barrel Length
L/22.5
Gun Length
2.82m (111.4in)
Weight in action
20,600kg (45,495lbs)
Elevation
-10 to +40 degrees.
Traverse
360 degrees
Shell Weight
27.23kg (60lb) AP (1.47kg of explosive)
27.23kg (60lb) Shrapnel (4.23kg of explosive)
Muzzle Velocity
396 m/sec (1,300 ft/ sec)
Maximum Range
9.14km (10,000 yards)
Rate of Fire
60 rounds per hour
The railway car was made up of five main parts. The gun was carried on a cast steel central section that was dropped down low to the track (the base of the pedestal was built into this section). This was connected to two steel two axle bogie sections, with platforms that were higher than the gun mount. The three sections were connected by two side plates.
There were three armored plates at each end of the car, and two more on the sides of the central section. In the raised position they provided protection for the crew, and were equipped with holes to fire machine guns through. In the lowered position they served as the fighting platform for the gun. In action the entire mount was lowered, and clamped to the railway track. There were side arms that could be extended to act as outriggers. There were six pads under the central section of the car which took the weight of the entire thing when it was lowered. It took 45 minutes to install the gun and 25 minutes to prepare it for movement.
The weapon had to be loaded at -10 degrees of elevation, and had a screw elevation system that could reach up to +40 degrees, using hand wheels mounted on both sides of the carriage. The gun was mounted on a pedestal that could be traversed using another hand wheel, and could traverse through 360 degrees.
The railway car was made up of five main parts. The gun was carried on a cast steel central section that was dropped down low to the track (the base of the pedestal was built into this section). This was connected to two steel two axle bogie sections, with platforms that were higher than the gun mount. The three sections were connected by two side plates.
Operational Use and Exercises
In practice, the 4.7-inch railway howitzers in Panama never saw combat, as there was no direct attack on the Panama Canal during World War I. However, they were actively used in training and defensive exercises. The Coast Artillery Corps units manning the Canal defenses conducted periodic drills to ensure readiness. It is likely that the railway-mounted howitzers took part in live-fire exercises to test their accuracy and the efficacy of using the railroad for positioning. For example, the guns might be moved to a prepared firing spur and directed at sea targets (such as towed targets in the ocean) or at simulated land targets along the coast. Such exercises would test the coordination between the artillery crews and the Panama Railroad engineers, and practice the rapid deployment of the guns from one side of the isthmus to the other.
Logs from the period (e.g. Panama Canal defense reports) indicate that ammunition was available and periodic test firings were done, both to calibrate the guns and to demonstrate defensive capability. These tests also helped work out any technical kinks in the M1917 mounts. Recoil and stability were important – crews had to ensure the railcar was securely anchored before firing. The howitzers’ moderate range meant they could not reach as far out to sea as the big 12-inch or 14-inch guns being installed, but they covered the closer approaches and could fire at a higher angle (useful if targets took cover behind terrain). They could also be used against land targets on shore – effectively serving as heavy field artillery if an enemy force attempted to land on Panama’s coasts.
No records of any emergency redeployment appear (since no attack came, there was no need to rush from one coast to the other in a crisis). But the mere presence of these mobile guns boosted the confidence in the Canal’s defenses. By November 1918 (the Armistice), the Panama Canal remained secure, and the railway guns had fulfilled their role of deterrence. After WWI, the need for temporary mobile guns waned as more permanent fortifications came online in the 1920’s. It’s likely the 4.7-inch railway howitzers were withdrawn or repurposed a few years after the war (perhaps sent back to the U.S. or kept in reserve).
Role in Panama Canal Defense System
The Panama Canal Zone’s WWI defense system was a layered one, and the 4.7-inch on M1917 railway mount fit into it as a flexible, medium-range component. At the top, the Canal had very large coastal artillery: for example, 12-inch disappearing guns and 12-inch mortars in concrete batteries (which were either in place or being installed by 1918). These could hit enemy warships at long range. On the lower end, there were field artillery and machine guns to defend the locks and land approaches, and smaller caliber anti-torpedo boat guns. The 4.7-inch howitzer sat in between – it had a longer reach and bigger punch than the field guns, but was more mobile (though shorter-ranged) than the huge fixed guns.
In the event of an attack, the plan would be that fixed guns at the main forts would engage enemy ships at long distance. If an enemy vessel slipped past or came in close, the mobile 4.7″ guns could be repositioned to ambush it from an unexpected angle. They could also reinforce whichever side of the canal was under threat. Notably, the Panama Canal could theoretically be attacked from both ends simultaneously (Atlantic and Pacific), so having at least one mobile battery on each end gave some tactical flexibility. Because they were on rails, these howitzers could even fire from multiple pre-surveyed firing positions: the defenses likely prepared several firing sites (with curved track sections or spur lines) where the guns could roll in and quickly open fire with coordinates already known. This way, a single pair of guns could cover a wider sector by moving between spurs. Documents from the U.S. Ordnance Department and Coast Artillery at the time emphasize such adaptability – railway artillery was seen as a way to “cover gaps” in fixed defenses and to respond to enemy movements unpredictably.
Logistically, the guns were transported to Panama by ship, likely as deck cargo or in disassembled form, and then reassembled on the Panama Railroad tracks. Once in the Canal Zone, moving them around was straightforward using locomotives. The presence of the trans-isthmus railroad (originally built in the 1850’s and upgraded during canal construction) was crucial – it essentially made these rail-mounted howitzers the quick reaction force of the Canal defense. An often-cited benefit was that they could be sent from Colón (Atlantic side) to Panama City (Pacific side) in only a few hours by rail. In an era before modern motorized artillery or air power, this rail mobility was a significant strategic advantage.
Historical Records and Legacy
Information on the 4.7-inch howitzer on M1917 railway mount in Panama comes from a combination of Ordnance Department records and later analyses by historians. For example, the U.S. Army Ordnance Department’s handbook and reports from 1917–1919 document the weapon’s specifications and note its deployment outside the continental U.S. The Report of the Chief of Ordnance and America’s Munitions 1917–1918 mention that a number of 4.7-inch guns were manufactured during WWI (over 200 were completed by 1919), and while dozens went to France for the fighting, others were held for home defense. Some of these indeed were diverted to the Panama Canal. Modern research compilations on U.S. coast defenses (e.g., Mark Berhow’s American Seacoast Defenses reference guide) also confirm that 4.7″ railway mount guns were part of the WWI-era armament of the Canal Zone.
Unfortunately, no known photograph clearly shows the 4.7-inch howitzer on its railway mount in Panama. Most Panama defense photographs in WWI focus on the big seacoast guns or the canal itself. However, one can imagine the 4.7″ on M1917 mount looking like a field gun perched on a rail flatcar, with perhaps a rotating base and rails extended to stabilize it during firing.
