In April 1945, an experimental Soviet spy-submarine helmed by Comrade Karpov crossed the English Channel when it intercepted a transmission claiming that Captain America and Bucky had been blown up. Not far from the region, the sub found the tattered body, his left arm of Bucky and fast charted the depths. Apparently flash-frozen in the oceans, the Soviets gradually increased his fever to thaw out his cells. Bucky was brought back from the dead after administering CPR, power and adrenaline directly into his heart. Bucky demonstrated a remarkable ability memories, while he had no memory of his previous life. He understood how to fight, and also how to speak four languages, but had no clue how he knew all this.
Fitting him the Soviets started work on the Winter Soldier Project. They started mental implantation to reprogram his thoughts and make him faithful to no one but the Soviets. On spy missions, the Bucky was sent out with the Winter Soldier to blend in with his environment and assassinate Cold War power-players. After performing oddly on a few missions, Bucky served as a body guard to the professor supporting the Winter Soldier project for a couple years before the Soviets decided to keep the Winter Soldier away in a suspended state until needed again, keeping his head from learning the facts.
Bucky's memory loss was so acute that even after killing a range of subjects including Red Skull and Nomad under the leadership of Karpov's prot??, Aleksander Lukin, the Winter Soldier came face to face with Captain America and still did not remember his past in any way.