Zond 3's design is typical of Soviet interplanetary craft of the 1960s. It echoes the Luna spacecraft of the same era, with a rocket engine at one end, a central section housing spacecraft housekeeping systems and an instrument cluster at the other end (on the right in this view).

Zond 1 headed off towards Venus in 1964, and Zond 2 was despatched towards Mars later the same year. Neither craft operated for more than a few weeks and were radio silent by the time they reached their destinations. Zond 3 was prepared for launching during the 1964 Mars launch window. However, there were delays and the opportunity to launch slipped by. In the event it was launched during 1965 towards the orbit of Mars although Mars was elsewhere by the time Zond 3 got there.

Its purpose was an engineering test of spacecraft systems following a whole series of Soviet interplanetary failures. In the event, Zond 3 was still operating when it reached the Martian orbit. In an engineering context, that made it the most successful Soviet interplanetary vehicle up to that time.

As it left the Earth, Zond 3 went past the Moon 1965 July 20 and took 25 pictures of the far side from distances ranging between 10,000 and 12,000 kilometres. To test Zond 3's communications system, The images were then transmitted back to Earth from a distance of 2,200,000 kilometres, and again from 31,500,000 kilometres.

Although it had no specific target of exploration, Zond 3 proved to the Soviet Union, and to the rest of the world, that its scientists were capable of building and operating an interplanetary craft. The success must have been quite frustrating to the scientists and engineers who put it together.