Dear ruth (1947)

Lt. William Seacroft, on leave from the Italian front, arrives at the New York home of Ruth Wilkins, with whom he has been corresponding. Unknown to both Ruth and Bill, Ruth's younger sister, Miriam, has been writing the letters and signing Ruth's name as part of a program to keep up soldiers' morale. Although Ruth has just gotten engaged to a coworker, she agrees to see Bill and pretend she wrote the letters.