But 65 years on, he is still haunted by what he saw -- memories that have only grown more terrible as he learned the camp's story.
Some 1.1 million people died at the camp between 1940 and 1945 -- one million of them Jews from across Nazi-occupied Europe. Some died from overwork and starvation, but most were murdered in the gas chambers.
"I will remember those things until the end of my days," the 86-year-old veteran, who headed a gunner unit of the Red Army's 322nd rifle division that liberated Auschwitz, said in interview with AFP at his home in Moscow.The sprightly, grey-haired veteran sat in his neat apartment surrounded by books and photographs, including one of him with Russian Prime Minister Vladimir Putin. A jacket pinned with war medals hung on the wall.
Martynushkin said it was only when he saw the camp's barbed wires and his commander ordered the troops to hold their fire that he "guessed that this was some special military zone, that this was something else."
For many veterans, the lack of shooting on that day -- January 27, 1945 -- in the midst of the fiercest weeks of fighting, remains one of their most powerful impressions, Holocaust researcher Ilya Altman told AFP.Martynushkin recalled the ghostly quiet and acrid "ash- and smoke-filled" air at Auschwitz.
He had seen other Nazi prisoner camps but as his unit moved along the perimeter of Auschwitz he was staggered. "It was huge. It went on and on for kilometres," he remembered.
"We started to see groups of people when we reached the fence. They came up to us dressed in prison stripes, some had other clothes on top," he said.
"After being in such a hell, constantly threatened by death, they were worn, depleted people. The only thing to them were those eyes that reflected a kind of joy -- of being freed, the joy that hell had ended and they remained alive."
As the Soviet troops closed in, some 60,000 prisoners had been driven back behind the Nazi lines in a forced "death march" that would be remembered by the survivors as worse than all that had come earlier at the camp.
The few thousands left behind were thought too weak to march but by some luck escaped being shot in the chaos of the rushed exodus.
Martynushkin turned 21 just days before arriving at Auschwitz, but by that time he had already spent three years at the front.Desensitized by the scale of suffering he witnessed over the war, he did not realize the full horror of the death camp, he said.
It was only later, when the Nuremberg trials began, that he came to understand what had previously seemed unimaginable.
"Back then when we saw the ovens, our first thought was: 'Oh well, so they are crematoriums. So people died and they didn't bury them all,'" he said."We didn't know then that those ovens were specially built for the killing of people, to burn those who had been gassed, that kind of systematic killing."
Auschwitz operated from 1940, a year after the German invasion of Poland. Its victims also included 85,000 non-Jewish Poles, 20,000 gypsies, 12,000 non-Jewish other European nationals and around 15,000 Soviet prisoners of war.
"It was unlike any other war. It was a war over the existence of entire peoples," Martynushkin said. "We were able to see this plan at Auschwitz. Everyone was there, representatives of all the European nations."
He was planning to travel to Poland with a handful of other surviving Soviet soldiers for the 65th anniversary of the day they liberated Auschwitz.