My father's godmother's husband fought in WW2 in the ranks of both Red Army and Waffen SS.
Quick history lesson: the Baltic States including Estonia were first occupied by Soviet Union in 1939-40, then by the Nazis in 1941, and then by the Soviets again in 1944. Obviously most Estonians didn't want anything to do with either regime. Nonetheless, this relative of mine filled 17 during the Nazi occupation and went to the police station get his first adult ID, but they just took him to the back room and they thanked him for volunteering to the glorious Waffen-SS. He said he was really upset because he came in his best sunday wear, too. He received training in a camp in Poland and fought on the Eastern Front for some while, until 1944. When the frontline was pushed back to Estonia, he dumped his uniform, acquired some civilian clothes and managed to get back home. Almost got caught by NKVD, too, who identified his German standard issue underwear. A fellow Estonian intelligence officer talked them out of arresting him. He was able to stay at home for a little while, helping his family with harvesting crops, until some Soviet activists drove by in a car and saw, hey, an able bodied kid doing farmwork instead of protecting the glorious Motherland. So they grabbed him right there, put him in uniform, and pretty much straight to the Estonian division in the Red Army.
He took part of some heavy, heavy fighting in Courland region, so heavy actually that he was only one of two survivors in his whole platoon. He credited his survival to being only around 5"2' and thus so much harder to hit. Nonetheless, he received a concussion and was hospitalized in Leningrad for some while. While he was hospitalized, all of his battalion had switched sides to the Germans (as the Estonian soldiers who made up the division had previously been treated as Gulag prisoners, until they were deemed useful/loyal enough to put on the frontline). He didn't even have anything to do with that, but being from that battallion and people in his village knowing that he had been with the Germans, meant that he couldn't go back home. So after the war ended, he didn't even return, but volunteered for professional military service in Russia. He served as an army NCO and a drill instructor in Russia for several years, just about until the death of Stalin, before he could come back, and marry his girlfriend. For what it's worth they're both still very happily married.