PL-37

URSS - Light Artillery Wagon (BP-35 Train), c24 built 1939-41

Legkaya Broneploshadka PL-37

Cutaway, from history.net (pinterest)

Trains proliferated through the 19th century and from transports migrated as mobile combat systems, as shown in the American Civil War or more recently in the Boer War. But these were one-offs created with whatever material was available for specific situation. Perhaps the first true tinkering about armoured trains was devised in Austria following the Hungarian Revolution of 1848. But they reached new heights in World War I in particular on the Eastern Front where they proved invaluable. Both the Austro-Hungarian and Russian armoured trains roamed the railroads in supported of their respective armies far from any base and rushed at unexpected places, bringing both troops and artillery support with them. After the 1918 armistice, the Russian Civil war saw more armoured trains being use by both Red and White armies as the network became a strategic asset to defend and expand. Armoured trains also defended a new Poland and left an immense impression on these eastern belligerents.

Albeit a bit forgotten in the interwar (apart in Poland where the development went on and a true strategy was worked on around), Soviet planners did not pursued much the concept, apart the use of fast, autonomous draisines that could perform the same tasks as a tank or armoured car on tracks. Japan on its side would even go furher a create a range of convertible road/rail vehicles. In 1939, with the war returning on several fronts for USSR (winter war in Finland, mandchuria-Mongolia border with Japan), it became urgent to rethink railroads in a more proactive way, in defence and attack in addition to classic reinforcement role of troops and tanks to the frontlines.

In late 1923, all remaining armoured trains were controlled by the Main Artillery Department, considering them as "guns on rail cars" usable in waritme, and no progress were made afterwards. On February 1930 however the Department of Motorization and Mechanization of the Red Army enquired about building new armoured trains for any possible emergency. In 1931, the Order of Battle of the RKKA described the combat tasks of such new armoured train. It was understood that dependong on their artillery, they would be classed into light and heavy units. They were also to operate as part of a battalion with two light and one heavy armouyred trains, reflecting on the nature of their wagons. In wartime they would bring good support for land forces. But on the Far East marked by poor communications, they cwould become the very core of any task mobile force with the railroad as its lifeline.

After series of more or less convincing armored draisines this was the return indeed of armoured artillery wagons in order to better defend army trains. Many models were devised in WW2 and USSR made more than any other belligerent, as they were superbly suited for the immensity of the flat plains of western and central Russia, but also down south in Ukraine. There was, wit the German invasion of the summer 1941 (Op. Barbarossa) even a renewed emphasis on anti-tank and anti-aircraft capabilities. After Barbarossa there were a flurry of adèhoce improvized trains, but the Army staff standardized four main production designs from 1941 to 1945. To the Pre War BP-35 and wartime PL-37, then BP-43, was added the NKPD-43 (simplifed BP-43), and OP-3, much simplified BP-43 using T-34 turrets. They also had both AA and rocket launchers to boot. As part of the BP-35 was a particular wagon which became its standard light artillery wagon: The PL-37.

BP-35 armoured train, with an early AA wagon and PL-37 behind.

The Military Stores No60 ("bronerembaza NKO No6") at Bryansk was responsible for the first of such models in 1933, the BP-35 armoured train. It was composed of a PR-35 armoured locomotive (with AA turret and radiostation) as well as two PL-35 light artillery wagons (two 76mm m.1902/30 guns) or PT-35 heavy artillery wagons fitted with a single 107mm m.1910/30 gun as well as a specialized SPU-BP AA armoured wagon plus 3-4 utility flat cars, to transport spare rails, a workshop and a conventional train in assistance, notably to feed, house and care for the armoured train crew. There were also smaller trains generally making the link between the BP-35, their base, and its distant rear base for supply.

The base train associated with a BP-35 comprised a HQ-wagon, medical wagon for infantry, a kitchen, laundry, and sleeping wagons for the crew of the armoured train. Each armoured wagon with artillery, light or heavy also had four Maxim MGs in addition, covering the flanks in ball mounts. Guns were always in turrets. The armoured locomotives were provided feeders to cross 120km at a top speed, at 45kph (yes, these were lumbering beasts). 10 tonnes or coal or 6 tons or black mineral oil were carried for a total weight generally contained below 400 tonnes. It had also a reocnnaissance part, a platoon of railway (draisine) armoured cars. The BP-35 unit thus was screened forward and at its rear by two light BA-20zhd and 3 medium BA-6zhd or BA-10zhd, while armoured flat cars hosted 3 rifle platoons. Production of the BP-35 started in 1933 at the Bryansk machinebuilding factory "Krasnyj Profintern" and 47 were in service in the summer of 1941, making the bulk of Soviet armoured train units. The factory was however evacuated in August 1941 and production stopped. New units would be planned in Ural factories.

In 1941, there were 34 light and 19 heavy armoured trains in total, including some 106 armoured wagons. Unlike the RKKA, the NKVD was tasked of police actions and only used autonomous draisines. They also used older Civil War preserved armoured trains to police the interior. In this general picture, the PL-37 was a modernization of the PL-35 light artillery wagon. I is assumed that c27 PL-35 were built, mostly differing by their older 76,2mm 1902 gun turret, whereas the PL-37 had the modernized 1902/30 variant with anti-tank rounds.

Design of the PL-37

The PL-37 was the standardized "light" (77 tonnes FL) artillery wagon of Soviet light armored trains from 1939 to 1941. About two dozen were built according to most sources, manufactred at the Krasny Profintern Plant, Bryansk for the BP-35 armoured trains. This two bogies, eight wheels flatbed was topped by a tall armoured structure with flat sides, close to the PL-35, with modest changes in construction, notably its new and dedicated turret and superstructure, roomier and lighter than usual tank turrets. The wagon was still fairly large, but came up with little free space inside. The main reason was because of its generous ammunition stowage. It was always camouflaged in various patterns which depended on the unit, season and area, and often presented a pattern of black and sand over standard army olive green.

As all wagons of that type, it was a symmetrical one, with two turrets forward and at the rear defining its main features, and a central observaiton post, raised above the roof line, with six sight slits on either side, and a taller central observation tower placed at the same level as the turrets. Both turrets were of simplified construction like the rest of the wagon, of riveted plating on steel and iron framing. The main casemate rested on a lower part seating on the flatbed, dotted with access traps for maintenance. There were two main access doors on the middle. Hatches were used on the roof to access the turretss which both had rear opening doors.

Being a pure wagon, the PL-37 was completely unpowered, apart a small petrol engine to power on board electric lighting. The 55 tonnes wagon was "free rolling". The turrets were hand-cranked s the elevation. The MGs were shoulder-manned. Observation was done from the central area, just standing out. The sides were a bit lower. The commander stand on top of a central raised platform with a small bunk in an observation used for all-round observation, hatch on top, with triplex glass visors for the two turrets, and a PTK panoramic periscope for the commander. It is not clear how orders were passed on from the observation tower to the two noisy turrets though, but by voice relay.

Armament and protection

The wagon did not featured sloped sides, and the riveted plating was an issue in case of a hit, possibly shrapnel only limited by the armount of internal spall lining. The armour was ranging from 0.78 inches for sides (20 mm) to a 0.59-inch (15 mm) roof. Ntural internal lighting was poor, only coming from the six upper slight slits, and side ball mounts and turrets. It was very dark inside. There were no sliding observation ports. The two enclosed turrets, with faceted sides, sligtly sloped roof, and observation top.

Each turret housed each a standard Soviet 76.2 mm (3 inches) M1902/30 field gun. A pre-WWI imperial model modernized in 1930, called in 1939 the 76 mm divisional gun M1902/30, it was still in larges numbers (2000+ in 1941), modernized at Perm in 1931-37. It fired HE rounds as standard, but in 1935 was introduced a new 6.3 kg armour-piercing (AP) capable of penetrating 56 mm armour at 500 m under, on a 30° plate, and 49 mm from 1,000 m and same. It could thus defeat anything short of the later Panzer IV. The standard was the fixed QF 76.2 x 385mm R, 7.5 kg (17 lb) round, with a rate of fire of 10 to 12 rounds aminute and inital muzzle velocity of 662 m/sec (2,172 ft/s), max range 13.29 km (8.25 mi). 280 rounds was provided by turret, operated by 6 men.

This was completed by the four 0.76 mm (0.3 inches) standard liquid-colled Maxim Machine gun, also legacy of Imperal Russia in huge quantities. It was still produced under licence and maintained. They were posted on each half-hull sides fore and aft in casemated recesses with ball mounts. They needed constant greasing to avoid being stuk with high temperature gaps. A drinking water tank was needed both for them and for crew's own supply in action. So with 12 men for the turrets, four for the MGs, there were still 16 remaining (crew of 30). They were likely the commander, his aide, two gunnery officers, and c12 loading assistants.

Specs.
Dimensions	48 feet 2 inches x 9 feet 9 inches x 14 feet 5 inches
Total weight	Chassis 55 tonnes, 77 tonnes fully loaded
Crew	30 (see notes)
Suspension	Diamond two-axle truck type
Range	120 km at top speed (loco supply dependent)
Armament	2x 76.2 mm M1902 field guns, 4x Maxim 7.62mm LMGs
Ammunition	560x 76.2 mm shells, 30,000 7.62 mm rounds.
Armor	78-inch sides, .59-inch roof
Total production	c24

Combat Use

Each "light" armoured train had two PL-37 light artillery wagons as said, and the 30-man crew found the interior quite cramped. The last PL-37 were completed in the summer of 1941, for about 12 light armoured trains or mixed compositions. But the German offensive signed their quick demise. The Luftwaffe in the first weeks raigned supreme, and these lumbering beast, at 40-45 kph, were easy pickings, especially at a time AA defence was limited at best to one or two quad-mounts for Maxim MGs. They were powerless against a diving stuka. When not destroying bridges, rendering these trains stuck in place to be later captured, they rarely met enemy armour and were most often dealt by artillery. It is likely most of the BP-35 armoured trains were lost in that summer, and the few surviving PL-37s ended in the next PL-43 trains.