Besides the series-produced Type 603, some additional prototypes were developed and extensively tested at the factory of Tatra in the first half of the 1960s.
Compared to the standard version, the onetime-built four-door sedan, with the identification number 0001-A, had a significantly more elegant and graceful appearance. In short, the design deserved the grade “very well done”. The prototype got a totally different designed car body without any large curves. Both silhouettes showed only little common characteristics - like the deep drawn fenders at the rear of the car - but as much more differences. This created the impression that the prototype was not drawn by the same designer, who created the design of the standard 603. Due to its sportive design, it might be also possible that Tatra charged an external, renowned car body designer, who approached his task totally unbiased. The elegance that radiated from the front continued seamlessly with smooth lines over the whole car until the rear end. Absolutely nothing was carried over from the bulgy and round appearance of the standard 603! Also the design of the sideways window line testified a sensitive hand of the designer, which peaked in a flatly running out angle of the rear window. The rear end of the four-door sedan was mainly characterized by a completely continuous rear light, which was reminiscent of US-American cars.
Nevertheless all these harmoniously visual refinements obviously could not convince the management of Tatra, thus the prototype remained a unique copy, which has survived to this day.