The Panama 14-inch M1920 Railway Gun Train

(Deployment: Panama Canal Zone During World War II)

During World War II, the U.S. Army’s Coast Artillery deployed a massive railway gun train in the Panama Canal Zone. Despite being commonly called a “16-inch” gun train, it actually centered on a 14-inch M1920 railway gun – one of the largest mobile artillery pieces of its time. The train was composed of several specialized cars operating on the Panama Railroad’s broad 5 ft gauge tracks. In Panama’s fortified spur lines (e.g. those at Fort Grant and Fort Randolph), this “rolling fortress” was kept ready to shift between the Atlantic and Pacific coasts at a moment’s notice. Below, we describe each major component of the gun train in detail – from the locomotive that hauled it, to the gun carriage and support cars – with emphasis on their technical specifications, roles in deployment on the fortified spurs, special adaptations for Panama’s conditions, and operational procedures. (Notably, unlike field-deployed railway batteries, the Panama train omitted any crew accommodation or barracks cars, since personnel were housed in fixed garrison facilities at the forts.)

ALCO 2-6-0 “Mogul” Type Steam Locomotive (“701-class”) (5-ft Broad Gauge)

The Panama Railroad relied in broad-gauge (5 ft) 2-6-0 “Mogul” type steam locomotives as its primary motive power for heavy trains during this era. Around 140 Moguls (100 built by ALCO-Cooke and 40 by Baldwin) had been purchased during canal construction (1904–1914), and these remained the workhorses into the 1920’s–30’s. After World War I, the Panama Railroad inherited many of the Isthmian Canal Commission’s 2-6-0 engines. These were oil-fired(standard for Panama) and equipped with slope-back tenders with two-axle trucks for bi-directional use, well-suited to the 50-mile line across the Isthmus.

In the late 1930s, as these engines aged, the railroad ordered five new “701-class” steam locomotives (delivered 1939–1942) to modernize the fleet. Despite the new class name, these were still 2-6-0 Moguls (upgraded with superheaters). The 701-class engines (numbered 701–705) were used in both freight and passenger service. Heavy-duty tasks – such as long freight drags of wartime supplies – were handled by double-heading Moguls if necessary. These World War II locomotives fleshed out the Panama Railroad's stud with superheated Moguls that delivered a healthy increase in power. Alexander Saunders noted that they had the"greatest tractive of any [Isthmian or Panamanian] steam engines." They weren't fast, A"but they can do a good job in steady running." They were not specialized military designs, but high-power standard-gauge locomotives chosen to handle the steep grades and 500+ ton trains associated with the 14-inch guns.

GE Diesel-Electric Locomotives (“401-class”) (5-ft Broad Gauge)

During World War II the Panama Railroad saw a massive surge in traffic (freight ton-miles jumped nearly 500% by 1943) as it hauled troops, equipment, and supplies to protect the Canal. To keep up, the railroad also purchased its first diesels in 1940 (five 95-ton GE locomotives, numbered numbered 401–405) for extra freight capacity.

Each delivered about 1,000 horsepower and rode on B-B trucks (two powered axles per truck). These diesels were built through the ALCO-GE collaboration and were among the earliest road switchers deployed in U.S. defense installations. (Notably, the Panama Railroad’s Panama Canal Review describes them as “1,000-horsepower, 95-ton diesel-electric locomotives”

Even so, steam Moguls remained in front-line service through the war.

Front Idler Flatcar (Buffer Car)

Additional to the often reported 5 car gun train, it is rarely mentioned that at least 1 Idler Buffer Car needed to be added to this consist at a minimum to keep the gun barrel from hitting the top of a boxcar or locomotive tender in front of it. Most often two of these flats or gondola buffer cars would be stored at a remote location to the gun (at the fort or ammo dump), and only be brought forward to the gun when needed to deliver ammo from the dump or spare parts.

Its role in this Gun Train configuration was only two fold:

A front Idler car allowed the long railway gun barrel to extend out over the flat without the barrel colliding with a taller locomotive/tender top or the top of a boxcar.
for hauling extra accessories while moving and for hauling ammunition from the supply dump to the Ammunition Car when the fixed on a permanent mount.

This flatcar had no special designation (a standard heavy-duty flatcar), but it was a unique practice in all railway artillery trains to use idler cars as “spacers.” No modification to the flat was essential as in this usage it did not need reinforced couplers to handle the load and could carry a few spare rails, timbers, or nothing at all. It was positioned immediately in front of the gun car during gum movement when mounted on its railway chassis.

Many photos show an empty gondola car was substituted for use as a Buffer Car in cases where no weight restriction for bridges existed. The gondola would then handle light loads of extra equipment and spare parts.

Notice the standard Gondola used as the front Idler Buffer Car, and a standard flat used as the rear Idler Buffer Car in this California photo of the 14-inch M1920 Railway Gun arriving at Fort MacArthur through the 22nd Street railway underpass. The gun barrel extends out over the gondola, which is necessary as a spacer as the barrel would collide with any boxcar or tender.

The Popular Mechanics Gun Train (December 1934)

In December 1934, Popular Mechanics published an article titled "Gun-Train Guards Ends of Panama Canal," detailing the deployment and operation of the 14-inch M1920 railway guns designed to protect the Panama Canal. These massive artillery pieces were mounted on railway cars, allowing them to traverse the Isthmus of Panama via the Panama Canal Railway and be positioned as needed to defend both the Atlantic and Pacific entrances of the canal.

The article highlighted the strategic mobility of these "rolling forts," emphasizing their ability to relocate across the isthmus in approximately two hours. This rapid deployment capability was crucial for responding swiftly to potential threats from either ocean. The M1920 railway guns featured a unique design that allowed them to be lowered onto fixed emplacements for 360-degree rotation, enhancing their effectiveness in coastal defense.

Two of these guns were stationed in Panama at for use at Fort Grant and Fort Randolph in the Panama Canal Zone, where they could be moved to either coast on the Panama Canal Railway. The article included detailed illustrations of the railway guns and their operations, describing the engineering feats achieved to safeguard this critical maritime passage.

The Railway Gun Consist (Panama Canal Zone)

When these guns were deployed they formed part of a support train containing up to 22 cars of varying types for long distance movement. But once a Railway Gun was dismounted to a permanent mounting, the gun train that service it consisted of as few as five support cars. The consist included at least 1 M1 AP projectile car, 1 M1 HE projectile car, 1 M1 powder car, 1 M2 fire control command car, and 1 M1918 repair car as a minimum as shown below in a photo taken at Fort Erwin in California.

Battery Erwin's northern emplacement 9 July 1941. The gun is under camouflage netting. The five box cars are the support cars described above. Notice no siding exists to hide the Powder Car behind an earthen berm or alternate Powder and Shell Car order behind the gun for reloading. Image was taken by the California National Guard's 115th Observation Squadron. (National Archives and Records Administration)