The Zond program reference article from the English Wikipedia on 24-Apr-2004
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Zond program

The Zond program was a series of Soviet unmanned space missions sent to the Moon from 1964 to 1979. While the Zond program is considered here as a lunar program, it should be noted that Zond 1 was sent in the direction of Venus and Zond 2 in the direction of Mars. "Zond" is simply Russian for generic "probe" and covered different vehicle designs.

The later Zond missions (4-8) were tests for manned lunar missions. They were basically the Soyuz spacecraft stripped of its Orbital module to save weight, but including the Descent module and Service module. They were launched on the Proton rocket which was just powerful enough to send the Zond on a free return trajectory around the moon without going into lunar orbit (the same as Apollo 13 flew in its emergency abort). It could have carried 1 or 2 Cosmonauts. There were serious reliability problems with both the Proton rocket and the new Soyuz, but the test flights pressed ahead with some glitches. The September 1968 flight was the reason NASA flew Apollo 8 to the moon in Decenmer 1968 instead of the Earth orbital test which had been planned because the CIA knew what the Russians were planning to do. Had Apollo 8 not flown when it did, it is possible Russians would have been the first to fly around the moon in late 1968 or early 1969.