In the 1960s, the Soviet Union had a program to send cosmonauts to the moon. But it’s success was staked to the N-1 booster, which not only never successfully flew but in some expert’s opinion couldn’t work- the first stage design may simply have been inherently flawed. When the N-1 was cancelled, the Soviet Union didn’t attempt to build a heavy booster again until the Energia project of the 1980s.
But there was another possibility: an entirely alternative booster project, the UR-700, which was considered in the early 1960s but for a variety of mostly political reasons lost out to the N-1 as the choice for the lunar missions. Could the UR-700 have sent cosmonauts to the moon? It’s impossible to say, but it certainly couldn’t have flopped any worse than the N-1 did. It was based on clustering tankage and engines similar to the Proton booster, which had some teething troubles but eventually became a standard workhorse rocket for the Soviets. One intriguing feature about the UR-700 was that even if the Soviet Union decided to cancel or scale back it’s lunar program, as long as it continued to make the Proton it could have still retained the dormant capacity to build the UR-700. The same tankage and engines could even have been super-clustered into an even larger version, the UR-900, which could have supported an attempt at a manned Mars mission! If the USSR had had a heavy booster capacity by 1970, maybe the Apollo program wouldn’t have been gutted and manned space exploration wouldn’t have gone into hiatus for so many years.