The Class 06 Surprise Steam Locomotive The two units of the class 06 represent a superlative – they were the most powerful express steam locomotives built in Germany. Their origin goes back to 1934, when the DRG's main management, the German State Railroad Central Bureau for Engineering commissioned the purchase of two extremely powerful express units. They were to haul a 600 metric ton express train at 120 km/h / 75 mph on level terrain, be at least 135 km/h / 84 mph fast, and adhere to the standardization design principles. Finally, Krupp in Essen brought a design to fruition, which specified a length (locomotive and tender) of 26.520 meters / 87 feet due to the large boiler dimensions. This long super boiler was also used on the freight train locomotive class 45 developed parallel to the class 06. It therefore required running gear with four sets of driving wheels and a driving wheel diameter of 2,000 millimeters / 78-3/4 inches for the necessary maximum speed. Analogous to the classes 41 and 45 built at the same time, the boiler pressure was set at 20 bar / 290 pounds per square inch and the axle load for the driving wheels could be varied. By selecting other pivot points in the load balancing system, the axle load could be set at 18 or 20 metric tons to enable wider use of these locomotives. Three-cylinder running gear with two outer cylinders and a third inboard cylinder mounted horizontally and shifted to the front was used to achieve better weight balance and higher starting tractive effort. All of the cylinders had their own Heusinger valve gear, whereby the outer cylinders were applied to the second set of driving wheels and the inboard cylinder conversely was applied to the crank axle of the first set of driving wheels. Streamlining rounded out everything, whereby access to the driving wheels and the trailing truck was left open for the most part due to experience in the past. Considerable difficulties in the production of the boiler delayed starting operation of the two gigantic locomotives: on road number 06 001 until the early part of 1939, on road number 06 002 until even the summer of 1939. In retrospect, the impending war took the German State Railroad's focus off these two units. All the same, road number 06 001 was still tested starting in April of 1939 by the Grunewald Locomotive Testing Bureau for speeds of 80, 100, and 120 km/h / 50, 63, and 75 mph. On June 15, 1939 there was thus an operational test run with road number 06 001 and a train weight of 678 metric tons on the route Bebra – Frankfurt/Main – Bebra, whereby a cylinder performance of even 3,670 pounds per square inch was briefly reached. Boiler damage however ended the tests at the beginning of July of 1939 and they were not resumed due to the war. The German State Railroad then stationed both units at the Frankfurt/Main 1 maintenance facility and they were used on the routes to Erfurt and Würzburg. Yet due to frequent boiler damages there were longer and longer downtimes. Both units survived the end of the war in storage, road number 06 002 even survived a bomb hit. An overhaul of these locomotives was not done since the subsequent DB saw no possible way to use these two giants. This story ended in 1951 with their retirement.