Soyuz 18-1 was launched April 5, 1975
and was meant to be the second mission to Salyut 4
. Instead after a problem during second and third stage seperation, the mission had the first abort before orbit insertion. The crwe experienced a 20 G reentry and landed in Chinese territory.
On board were Vasili Lazarev and Oleg Makarov. Their callsign for the mission was Ural (Urals).
All was going well on the flight up until 288.6 seconds after launch when the rocket was at an altitude of 192 kilometres. At this point the second and third stages were meant to seperate. This involved the release of six locks. However only three released. But the third stage still ignited. This thrust (as well as the heat probably) caused the last three bolts to release.
You would think that this would have been the end of the problems, but this was only the start. The breaking free of the second stage made the third stage enter an attitude outside of the accepted range intiating an abort at 295 seconds after launch. Because the third stage was already pointing downwards, the extra thrust the the Soyuz spacecraft used to seperate itself the rest of the rocket caused the capsule the accelerate towards the ground.
This meant that instead of an expected 15 G, the cosmonauts experienced a reentry that topped out at 21.3 G. The landing systems worked properly and the crew were able to land, but what they didn't realise was that they had landed in the China-Mongolia border region, 80 km from Soviet territory (officially it was said to be in the Altai mountains).
Due to the remoteness of the region, they were able to be retrieved only a few hours after touching down, without the Chinese or the rest of the world being any the wiser. The capsule was recovered the following day.
All this occurred three months before the Apollo Soyuz Test Project. It further heightened the fears of some people in the US that the Soyuz spacecraft was not safe. After some 'encouragement' the Soviets finally revealed that it was an early version of the rocket that "less diligently checked" than the one that would be used by Soyuz 19.
In all the flight lasted only 21 minutes 27 seconds, the longest non orbital spaceflight flown.
Western sources tend to refer to his flight as Soyuz 18-1 or 18A, while the Russians call it the April 5th Anomaly.
All this was not made public until 1983 in the Soviet Army newspaper "Red Banner".