Ambush in Odessa

"Five years ago, I was escorting a nuclear engineer out of Iran, somebody shot out my tires near Odessa. We lost control, went straight over a cliff, I pulled us out, but the Winter Soldier was there. I was covering my engineer, so he shot him straight through me. A Soviet slug, no rifling."

- Natasha Romanoff and Steve Rogers The Ambush in Odessa was a conflict that occurred in Odessa, Ukraine, where S.H.I.E.L.D. operative, Natasha Romanoff, was tasked with escorting a nuclear engineer to safety. However, the Winter Soldier, a HYDRA assassin, ultimately assassinated the scientist.

Background
"For seventy years, HYDRA has been secretly feeding crisis, reaping war, and when history did not cooperate, history was changed." "That's impossible. S.H.I.E.L.D. would have stopped you." "Accidents will happen.""

- Arnim Zola and Natasha Romanoff Following the Capture of Arnim Zola in 1945, Sergeant Bucky Barnes of the Howling Commandos fell off a train, and he was presumed deceased by those knew him. Unbeknownst to his colleagues, Bucky survived the fall due to Arnim Zola's experiments on him. HYDRA kept him their prisoner for many years, and was eventually turned into an assassin as he was the first test subject of the Winter Soldier Program. For the next several decades, Bucky would conduct HYDRA operations abroad, assassinating political and scientific figures who posed a threat to the terror organization.

Attack
In 2009, Natasha Romanoff was given a S.H.I.E.L.D. assignment to escort a nuclear engineer out of Iran as he was a potential threat to their enemies. She managed to escort the scientist out of the country, and she proceeded to make her way to the rendezvous point. However, HYDRA dispatched the Winter Soldier to eliminate the scientist; he intercepted the S.H.I.E.L.D. assassin and the scientist near Odessa, Ukraine, where he blew her tires out and forced them off a cliff. Natasha managed to pull the injured engineer out of the wrecked car, only for the Winter Soldier to proceed by shooting Natasha in the abdomen with an untraceable Soviet slug. The bullet entered the scientist, killing him. Having successfully eliminated his target, the Winter Soldier made his getaway without pursuit.

Aftermath
"Going after him is a dead end. I know, I've tried."

- Natasha Romanoff and Steve Rogers

Black Widow's first encounter with the Winter Soldier ultimately prompted her to hunt him down and uncover his true identity. However, she ultimately realized that he was more of an elusive enemy that she had ever encountered. Despite her desire to expose him and figure out his identity, she ultimately accepted that pursuing him was a dead end. Even most intelligent communities doubted his existence, with the few that did believe that he existed only knew him as the "The Winter Soldier."