The center cab hydraulic DD51 had two engines (1100PS x 2) at the front and rear, and was expensive. So the idea was to have a single engine with around 2000PS, making it more economical to buy. At the time, West Germany and Japan were the only countries that had put hydraulic transmissions of over 1000PS into practical use, but Germany had developed a hydraulic transmission with over 2000PS. So the box-shaped DD54 (1820PS x 1 engine) was built using German technology. However, the German hydraulic transmission for standard gauge trains was not suitable for Japan's narrow gauge. Due to intellectual property rights and insufficient communication with the German manufacturer, the propeller shaft broke and pierced the ground, creating a pole vaulting situation. The DD54 was the most surreal and metaphysical of all Japanese locomotives. It was four years later that a hydraulic transmission with over 2000PS was made in Japan.
Odakyu Electric Railway's SE car is a Romancecar (Class 3000, SE = "Super Express") for express trains built in 1957. In addition to its articulated bogies, light weight, and low center of gravity, the super streamlined carriages reduced air resistance and recorded the world's fastest speed (145km/h) for a narrow-gauge railway at the time in high-speed tests. So when the Japanese National Railways (JNR) was planning the Shinkansen, they tested this carriage and used it as reference for various things. I actually rode it, and it ran at about 80km/h on the Odakyu Line(:Private railway from Tokyo to Kanagawa prefecture). That's because the Odakyu Line was always crowded. I remember thinking, "Hmm... let me think about it for a bit!"