Premise: The Key is a 1958 British war film set in 1941 during the Battle of the Atlantic. It was based on the 1951 novel "Stella" by Jan de Hartog (later republished as "The Distant Shore" and "The Key") and was directed by Sir Carol Reed. William Holden, Sophia Loren and Trevor Howard starred in the production.
Hypothesis: Loren's work as an actress was most widely appreciated in the mid-twentieth century.