You’ve probably heard of conspiracy theories that the moon landing was a hoax (those are false, and easily debunked). But have you heard the one about how the moon race was itself a hoax, because the Soviet Union was never trying to get to the moon in the first place?

Or at least, that’s what the Soviets claimed to cover up their unsuccessful lunar-landing program. It was a lie that held fast until 1989, when a group of American aerospace engineers went to Moscow and finally saw the Soviets’ failed lunar-landing craft for themselves.

President John F. Kennedy kicked off the moon race in 1961 by announcing the U.S. would put a man on the moon by the end of the decade. From then on, NASA’s program to reach the moon before the Soviet Union was public information. In contrast, the Soviet Union didn’t publicize its own program, or even officially admit it had one. After the U.S. reached the moon on July 20, 1969, the Soviet Union continued its lunar-landing program into the early ‘70s while still publicly denying its existence.

At first, “secrecy was necessary so that no one would overtake us,” wrote journalist Yaroslav Golovanov in the Soviet newspaper, Komsomolskaya Pravda. “But later, when they did overtake us, we had to maintain secrecy so that no one knew that we had been overtaken.”

Soviet spokesmen also said the country was more interested in creating satellites and sending robotic probes to the moon than manned missions that risked human life. In broadcasts to Latin America, Africa and Asia, Radio Moscow framed Apollo 11 as “the fanatical squandering of wealth looted from the oppressed peoples of the developing world.”

For many Americans who worked in and reported on aerospace research, this denial was never believable. One of these Americans was James Oberg, a NASA space engineer from 1975 to 1997 who speaks Russian and has written multiple books about the U.S. and Soviet space programs. In 1979, he wrote an article for Reason Magazine arguing, “Many of the same elements that characterized preparations for the Apollo moon landings also showed up in the Soviet program.” He also noted that Soviet cosmonauts during the 1960s spoke as though they were in a race with the U.S. to the moon.

“I can positively state that the Soviet Union will not be beaten by the United States in the race for a human being to go to the moon,” said cosmonaut Vladimir Komarov in 1966, a year before his tragic death during reentry. “The U.S. has a timetable of ‘1969 plus X,’ but our timetable is ‘1969 plus X minus one’!”—i.e., the Soviets would make it the moon a year before the Americans.

Yet some conspiracy-minded Americans were swayed by the Soviet Union’s propaganda, and began to suspect the U.S. government had invented the competition in order to rationalize the enormous financial investment in NASA’s moon mission.

Unlike modern moon-landing deniers, many prominent moon-race deniers held influential positions in politics and media. Senator J. William Fulbright said in 1963 that “the probable truth is that we are in a race not with the Russians, but with ourselves.” And in a 1964 editorial titled “Debating the Moon Race,” The New York Times wrote, “There is still time to call off what has become a one-nation race.” On the moon landing’s fifth anniversary in July 1974, CBS anchor Walter Cronkite told America, “it turned out that the Russians were never in the race at all.”

In truth, the Soviets were in a moon race with the U.S. during the 1960s, and they were fairly confident they could beat the Americans because “they’d had all the firsts,” Oberg says: they had the first satellite, the first probe to land on the moon and the first man and woman in space. In fact, the Soviets thought the U.S. timetable for reaching the moon was just propaganda because it seemed too ambitious.

When Apollo 11 really did land there in 1969, just eight years after JFK’s announcement of the country’s intentions, Oberg says the Soviets “slowly came to realize they’d woken the sleeping giant; that they had driven the U.S. government insane enough to spend absolutely crazy amounts of money to do this.” Still, the Soviets continued their lunar-landing program into the early ‘70s because they didn’t know if the U.S. would continue its lunar exploration.

“If the Americans had a setback and quit or just got tired and stopped, then [the Soviets] could move in and outdo American lunar flight,” he says. “But by 1972, they realized that they just couldn’t build the rockets or the spacecraft reliable enough to do that.” Though they did build a lunar lander intended for cosmonauts to use on the moon, they couldn’t reliably send it there.

The fact that the Soviets had built a lunar-landing craft intended for the moon remained a secret until 1989, when American aerospace engineers from the Massachusetts Institute of Technology received a tour of the student engineering laboratory at the Moscow Aviation Institute. Even then, the revelation was kind of an accident, says Laurence Young, who was one of the engineers on the trip and is now the Apollo program professor emeritus of aeronautics and astronautics at MIT.

The MIT delegation had traveled to the Moscow Aviation Institute to discuss possible joint educational programs between the universities. This was during the waning days of the Soviet Union and the period of glasnost, or “openness,” when the country was sharing more information with the U.S. During the meeting, the Soviets took the Americans on a tour of a large hall filled with older spacecrafts that they used as a teaching laboratory.

“It was in the course of going through that hall that Ed Crawley [another MIT engineer] and I saw this spacecraft,” Young says. “I said, ‘What is that thing that sort of looks like our lunar insertion module?’” The Soviets replied that it was their own lunar lander. Young pressed them, saying they must mean it was their design of a lunar lander, not that it was an actual craft they had intended to send to the moon.

“They said, ‘Da, da!’ That was the lander that was going to go to the moon,” he says. “I didn’t know whether to believe them.”

Young and his colleagues had assumed the Soviet Union had a program to send humans to the moon, “but we didn’t have any evidence,” he says. “That’s what made this completely accidental discovery…so amazing for us.”

The engineers took some pictures of the Soviet lunar lander and, back at MIT, the university issued a press release about it. On December 18, 1989, The New York Times—which had once accused the U.S. of running “a one-nation race” to the moon—ran a front-page headline declaring: “Now, Soviets Acknowledge A Moon Race.”