Background of the birth

Freight transport in JNR

In the world, a gas turbine for railroad was first applied to the locomotive power source. But in Japan, a gas turbine locomotive had not been planned. In 1960's the freight transport in Japanese National Railways was declining from year to year. Mass produced diesel locomotives such as type DD51 had already been becoming surplus.
After Japan Freight Railway took over JNR, more high power non-electric locomotive was required to resolve the double heading of DD51. But already diesel had the ability to resolve this and AC electric driven diesel locomotive, DF200 was developed

If the freight transport in those days did not decline and the rail transport remained to play a main role, an EF66 class non-electric locomotive may be required. To realize this class of non-electric locomotive, there were no other choice except for a gas turbine.
But like Union Pacific Big Blow, high performance diesel locomotives might have replaced them.

Speed up project for conventional lines

　In 1960s, a train's speed in Japanese conventional lines was gradually increased and reduced journy time. In 1966 diesel powered rail car kiha 82 enabled the limited express train network spread all over Japan. The maximum operating speed of the EMUs were 110km/h and DMUs 100km/h. Next speed up project targeted the maximum speed of 120km/h. EMUs already had the sufficient performance to achieve this speed but DMUs didn't. For this purpose, high performance DMUs, kiha 90 and kiha 91 were developed and they were expected to offer nearly similar speed to EMUs on flat routes. Based on these tests, series kiha 181 express train was produced and put into commercial operation.
Next goal was to speed up on curves because conventional lines especially in non-electrified areas had many steep curves and kept trains from speeding up.
To speed up on curves, a light weight and low center of gravity and centrifugal force free car was required. By using EMU system, many part of these issues were to be resolved, but DMU system in those days could not resolve due to its heavy and balky power source. To reduce the centrifugal force on curves, a tilting system was required. An active tilt system is better than a passive one but it was very difficult to build safe and reliable active tilt system. In Europe, APT, TGV and some other trial and plan had already existed to utilize the passive tilt system, but all of them gave up and abandoned.
In 1970, series 591 EMUs was built to test a passive tilting mechanism and articulated formation.
To overcome the diesel performance limitation, a turbine's high performance had come to draw a lot of attention.

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