Since the Bundesbahn decided at the end of the fifties to electrify all important main lines, the six-axle diesel locomotive was dropped from the program. It was intended for heavy express and freight trains and was to achieve an output of 3,200 hp. At that time, Henschel had already started developing the V 320 and was now continuing it at their own expense.

The locomotive drew its power from two sixteen-cylinder Daimler Benz (later MTU) engines with 1,600 hp each. The two propulsion systems were independent of each other and could also be operated individually. Since passenger trains were also to be transported, the maximum speed was set at 160 km/h and train heating was installed. The car body already had angular shapes, which were also found later on the V 160 and the class 218.

The locomotive was designated DH 4000 by the manufacturer and was leased to the Bundesbahn after internal testing. From 1968 it was listed there as the class 232. Despite its good performance in service with express and freight trains, it was returned to Henschel in 1974, as no purpose for diesel locomotives of this power class was seen.

This was followed by a rebuild to a pure freight locomotive, in which the maximum speed was reduced to 120 km/h and the train heating was removed. At the same time, the power per engine was increased to 1,900 hp. It was then sold to private companies, where it had to pull heavy freight trains. After being overhauled in Italy in 1995 and used there for some time, it was used by the German track construction company Wiebe between 1998 and 2015. Since 2020 it can be found in the museum in Wittenberge.

An almost identical locomotive was sold to the Soviet Union as the ТГ400 (TG400). Since they preferred diesel-electric locomotives and soon achieved comparable power outputs themselves, no more were ordered. Since China had not yet decided on a technology at that time, 30 units were bought. These were designated NY5, NY6 and NY7.

In search of more powerful diesel locomotives, the Denver & Rio Grande Western ordered three ML 4000 from Krauss-Maffei in Germany in 1961. With hydraulic power transmission and two high-speed Maybach engines with 2,000 hp each, their basic technical concept was completely different than that of American locomotives. The advantages lay in the better power-to-weight ratio and better traction properties of the three-converter transmission. In order to cover the development costs, Southern Pacific was persuaded to order three more ML 4000.

The operators' route network included passes in the high mountains over which trains weighing more than 10,000 tons had to be pulled. The problem turned out to be that the engines were designed for a full load share of ten percent according to German conditions. In the USA, however, this proportion is many times higher, which, in conjunction with the sometimes hot climate, led to problems. In addition, maintenance was found to be too complex compared to the much simpler American locomotives.

The problems were initially so serious only at the DRGW that its three locomotives were sold to the SP, while the SP ordered a second batch of 15 locomotives. While the first batch had a self-supporting car body, the second batch was built in the same way as American road switchers with a supporting frame and machinery covered by hoods. At the same time, the Brazilian Estrada de Ferro Vitória a Minas (EFVM) ordered 16 ML 4000 in meter gauge. 

Southern Pacific No. 9011 in August 1964 at San Jose, California

Drew Jacksich

Although the SP was initially happy with the ML 4000, problems with the air intake in the long tunnels of the Sierra Nevada soon became known. For the same reason, EMD developed some locomotives with modified airflow, which became known as “Tunnel Motors”. When the maintenance of the engines became too expensive, the locomotives were retired by 1968 with the conclusion that the hydraulic power transmission itself was reliable and economical. The 9113 was converted into a camera car in 1969 and is now owned by the California State Railroad Museum. The Brazilian machines, on the other hand, remained in use until the 1980s.

The Voith Turbo company had long been known worldwide as the market leader in the field of hydrodynamic transmissions and had supplied transmissions for locomotives and DMUs for decades. The company only started building its own locomotives in 2006, in order to put a gearbox developed in the nineties for an unrealized Vossloh diesel locomotive into circulation. This culminated in a purpose-built factory where the Maxima and Gravita were manufactured between 2006 and 2014.

The LS 640 reU2 gearbox made it possible to variably distribute the power to both bogies. With other, single-engine diesel-hydraulic locomotives, only the entire engine output could be reduced in case of wheel slip. In this case, the Maxima can continue to transmit power to the other bogie. The power required for the Maxima 40 CC, which was presented first, comes from a 16-cylinder engine from the Anglo Belgian Corporation, which, in contrast to the engines commonly used in diesel locomotives in Germany, is a medium-speed engine with a correspondingly large displacement of 255 liters. It thus develops a starting tractive effort of up to 519 kN, which, however, is reduced to 408 kN in practice. Due to the latest developments in the field of cooling fans and sound insulation, the Maxima was not only the most powerful single-engine diesel locomotive in Europe at the time it was commissioned, but also one of the quietest.

The second model offered was the Maxima 30 CC, which was manufactured from 2008 and was immediately popular with various customers. It also has six axles and has 2,750 kW from twelve cylinders. Due to the lower weight, the tank capacity has been increased from 9,000 to 10,000 liters. Although a total of 77 examples of the 30 CC and 40 CC had been ordered, production was stopped after just six and 13 examples respectively in 2014. The Maxima 30 LCC with 3,200 kW was offered as a further, unrealized six-axle variant. With four axles, there was the Maxima 20 BB with 2,000 kW and the 20 LBB with 2,400 kW. Although the four-axle variants were offered with an optional top speed of 140 or 160 km/h, they could not be sold due to the diesel-electric competition.

The Wehrmacht procured four diesel-electric double locomotives, which were to transport the gigantic 80 cm guns to their place of use and align them in position. These guns weighed 1,350 tonnes and required several trains to transport them. Although four double locomotives were planned, only two were completed, of which only one was actually used.

The guns were not railway guns in the true sense of the word, but rather stationary, which were only transported by rail and had to be set up on site. There, the crews of several construction trains created a spacious position with a double-track curved track to align the cannon. Although the fine alignment was done by electric motors under their own power, the locomotives were needed to move them on the curve of the track. Two of these double locomotives were provided for this purpose, which, thanks to their electrical power transmission, could also supply the current for the gun.

Each half had a six-cylinder in-line MAN engine that produced 691 kW (940 hp). Each of the four axles mounted in a frame had its own nose-suspended motor. A maximum speed of 75 km/h could be reached for transport to the position or other journeys.

After the locomotives were only rarely used during the war, the Bundesbahn subsequently took over two double units in their fleet and kept a third as a spare parts donor. In order to improve performance in freight transport, two Maybach V12s, each with 808 kW, were installed, as they were also used in the modern V 200. The locomotives were given the same red paintwork as the new-build locomotives and, according to the applicable scheme, were designated V 188 due to their original 1,880 hp total output. With the new scheme of 1968, they became the class 288, but the first locomotive was retired in 1969 and was not given a new number. The original D 311 04 and later V 188 02 a+b was renumbered 288 002 and was kept in stock until the beginning of June 1972.