A Kriegslokomotive usually had two classifications: one based on the normal peacetime classification system and a separate wartime classification. For example, a wartime steam locomotive or Kriegsdampflokomotive (KDL) was given a KDL class as well as its DRG (Deutsche Reichsbahn) class. Likewise a wartime motorised locomotive or Kriegsmotorlokomotive had a KML class number and a wartime electric locomotive or Kriegselektrolokomotive would have a KEL class number. Besides the DRG, the German Armed Forces had their own locomotive classes. A field railway locomotive belonging to the Army were known as a Heeresfeldbahnlokomotive or HF. Standard gauge engines for the Wehrmacht, mostly diesel switchers, were designated “Wehrmacht Standard Gauge Locomotive” (Wehrmachtslokomotive für Regelspur) or WR.

As German troops swept across Poland and Hitler began to prepare for Operation Barbarossa, the invasion of the Soviet Union, the Deutsche Reichsbahn was extended ever further east, while more troop trains, trains ferrying tanks and artillery pieces, trains fetching fuel, and trains supplying factories across the newly conquered territories pushed what was a well-run railway to unprecedented limits. With new lines laid quickly, the cry from operators in the east was for simple, strong engines with light axle loads. Fitness for purpose and simplicity truly were the keys to good wartime design. Even Wagner’s powerful and dependable class 44 2-10-0s were too heavy in axle loading and too complex for the rigours of wartime assignments.

Wagner responded with the class 50 2-10-0s, first built in 1939, rugged, two-cylinder machines with an axle loading of just 15.2 tons (anything under 18 tons is light). Weighing 87 tons and allowed to run at 80 kph (50 mph) in both directions, the class 50s were as popular as they were reliable. They were designated Kriegsloks and were among some seven thousand steam locomotives produced in Germany during just two and a half years of brutal conflict. Even so, the first class 50s were considered too complex for the kind of mass production that men like Wagner could never have envisaged in the 1920s. The revised class 50UK (Übergangskriegslokomotive, or transitional war locomotive), with fabricated welded construction replacing steel castings, was the result – yet even this was seen as too complex for the rapid production the government and military demanded. Cue the class 52, an austerity version of the class 50 and the archetypal Kriegslok, a steam locomotive prepared for all-out war as never before.

The class 50, however, continued to be built, with gaps, not just throughout the Second World War, but for a long time afterwards. The final members of the class were built, with modifications to the original design, by the East German Deutsche Reichsbahn at the Lokomotivbau Karl Marx in Babelsberg in 1960, by which time 3,164 had been produced. Class 50s continued in front-line service on the Deutsche Bundesbahn until the end of steam in 1977, and on the Deutsche Reichsbahn until 1987, two years before the fall of the Berlin Wall.

These engines were great travellers. Either seized by allied railway engineers or made over as war reparations, the class 50s could be found at work between the 1950s and 1970s in, among other countries, Austria, Poland, Denmark, France, Turkey, the USSR, and Norway, as well as throughout the Balkans. They may have been used for evil ends in the early and mid-1940s, but the steam locomotive is in itself an innocent machine, and the class 50 was much needed and much liked wherever it went.

The class 52 began service just as German expansion eastwards was grinding to a halt. In this sense, they were too late; yet few can doubt that, whatever the job they were asked to do, the locomotives themselves performed reliably and well. Brutes to look at, the class 52s were among the quickest of all steam locomotives to build. Records of exactly how many man-hours were needed to build a complete 52 are uncertain, but the production figures speak for themselves. Between September 1942 and May 1945, more than 6,300 had been put into service. More were built between 1945 and 1950, bringing the total up to what seems to have been 6,719. From 1960, the Deutsche Reichsbahn rebuilt 200 with new boilers, and a total of 290 with Giesl ejector draughting to enable low-grade coal to be burned efficiently.

After the war, the class 52s were dispersed throughout various parts of Europe, although it was somehow strange to see some of the very last of them working for the Polish railways. It was the invasion of Poland that had signalled the start of the Second World War and it was in Poland that the worst of the Nazi extermination camps were sited – and it was the 52s that had brought so many to their deaths there. But as an example of how a machine that was essentially the product of a long craft tradition could be transformed into a unit of mass production, the 52 remains a fascinating locomotive.

A heavier Kriegslok, the two-cylinder class 42, was built in much smaller numbers – 837 in 1943 and 1944, with further examples produced between 1945 and 1949 – to be used where limitations on axle loads were less demanding than on the eastern front. There was, however, a design for a much larger Kriegslok altogether. This was Adolf Wolff’s 1943 proposal for a 2-6-8-0 compound Mallet, a form of articulated locomotive with two engine units beneath the boiler, devised by the Swiss engineer Anatole Mallet. At 27.4 m (90 feet) long and weighing 140 tons, this impressive locomotive would have been a formidable performer, but by the time Wolff was drawing up outline designs the Borsig works had been severely damaged by allied air raids, and as 1944 dawned it was clear to most steam men – if not to Adolf Hitler – that the war was lost and that, as Germany fought an increasingly desperate rearguard action on two fronts, the production of weapons and ammunition would have to take over from that of locomotives.

One logical end of the Deutsche Reichsbahn Einheitloks (unified locomotive types) programme of 1923 was the class 52 2-10-0s, first steamed at Borsig works on 12 September 1942 in the presence of Albert Speer, Hitler’s minister for armaments and production. The class 52 Kriegslok (war locomotive) was designed for mass production in factories in Germany and in territories conquered through Blitzkrieg, the ‘lightning war’ of 1939–41 which brought much of Europe under the Nazi yoke. Between 1942 and 1945, a total of 6,239 class 52s were built, in twenty factories across Europe. This side of the Russian 0-10-0 standard freight locomotives, it was the biggest class of steam locomotives ever built.

The principal purpose of these brutally functional locomotives was to work freight and troop trains through the eastern front. Until the headlong German retreat of 1944, the Deutsche Reichsbahn’s track mileage had increased by 16,000 miles during the war. The class 52s were also used for the transportation, at a stipulated 45 kph (28 mph), of three million Jews, and others who fell foul of the Nazi regime, to concentration and extermination camps. Perhaps no other class of locomotive has been built for such savage purposes.

Such was the efficiency of the Borsig works that the first of the class was completed three months ahead of schedule. Speed was, of course, of the essence in wartime, yet the drive and ability to build so quickly was the result not just of the Einheitslok programme, which made locomotive building in Weimar and Nazi Germany a model of efficiency, but also of the creation of the Gemeinschaft Grossdeutscher Lokomotivfabriken (GGL) in 1942, as part of Speer’s new ministry founded earlier that year. The Nazi regime had taken absolute control of the Deutsche Reichsbahn, which had been established in 1922 as an independently run state business, able to raise its own finances. Now the GGL was to determine locomotive design and production. Perhaps it is not surprising that, in the wartime imagination, the class 52 had more than something of the look of a Nazi stormtrooper about it.

Detailed design work on the class 52s was led by Friedrich Witte. His predecessor, Richard Paul Wagner, architect of the Einheitloks programme, was forced to resign his responsibility for centralized Deutsche Reichsbahn locomotive design and production in the summer of 1942, as the Nazis tightened their grip on the railways. Hitler and Speer believed that the Deutsche Reichsbahn had been slack in its response to war demands, the Führer calling for steam locomotive production to be upped to 7,500 per year. This was an impossible figure, although production did increase from 660 in 1939 to a peak of 4,533 in 1943. Wagner, who had the responsibility of building up the Deutsche Reichsbahn fleet after some five thousand German locomotives had been packed off to the country’s former enemies as part of the war reparations demanded by the Treaty of Versailles, had been happy with an annual production of 800 new steam locomotives. Even so, that was only possible because of the standardization of design and construction. Significantly, perhaps, Germany built more steam locomotives in total – approximately 155,000 – than any other country except the USA, which produced around 177,000. Britain, a small country with a big empire, built 110,150, Russia around 50,000, and France 39,000. No other country came anywhere near these figures. According to Philip Atkins, former librarian at the National Railway Museum, York, 205 were built in South America, thirty-one in Africa, and, rather charmingly, just one in Portugal.