In 1955 Japan's Ministry of Trade and Industry proposed the concept of Japan having a small affordable National Car, something akin to the German "People's Car" concept which resulted in the Volkswagen Type 1. The proposal suggested that the car should be a 4 seater with an engine of between 350-500cc, a weight of about 400kg and a top speed of about 100kph. In response to this Prince built the DPSK prototype.

The specifications Prince came up with for the DPSK was a 495kg 4 seater car with a rear mounted 601cc air cooled horizontally opposed 2 cylinder engine called the FG2D, which produced 24hp at 4500rpm. This engine suffered from vibration and excessive noise issues and was eventually abandoned and replaced with the FG4C, which was a 4 cylinder horizontally opposed 599cc engine. This new 4 cylinder prototype was referred to as the CPSK. Prince persevered with this concept until 1959 when the whole National Car project was abandoned, most likely due to the fact that Prince were at the time positioning themselves in the market as a more upscale quality car manufacturer.