What film won the 1943 Oscar as best film

Casablanca
Because of its November 1942 release, the New York Film Critics decided to include the film in its 1942 award season for best picture.

Casablanca lost to In Which We Serve.

However, the Academy stated that since the film went into national release in the beginning of 1943, it would be included in that year's nominations.

Casablanca was nominated for eight Academy Awards, and won three.

As Bogart stepped out of his car at the Academy Awards ceremony, "the crowd surged forward, almost engulfing him and his wife, Mayo Methot.

It took 12 police officers to rescue the two, and a red-faced, startled, yet smiling Bogart heard a chorus of cries of 'good luck' and 'here’s looking at you, kid' as he was rushed into the theater."

When the award for Best Picture was announced, producer Hal B. Wallis got up to accept, but studio head Jack L. Warner rushed up to the stage "with a broad, flashing smile and a look of great self-satisfaction," Wallis later recalled.

"I couldn't believe it was happening. Casablanca had been my creation; Jack had absolutely nothing to do with it. As the audience gasped, I tried to get out of the row of seats and into the aisle, but the entire Warner family sat blocking me. I had no alternative but to sit down again, humiliated and furious...

Almost forty years later, I still haven't recovered from the shock."

This incident would lead Wallis to leave Warner Bros. in April.

Source: https://en.wikipedia.org/wiki/Casablanca_(film)#Awards_and_honors