Conversation so far:
When did Pamela Harriman marry Randolph Churchill?
Pamela Harriman married Randolph Churchill in 1939.
Did Pamela Harriman and Randolph Churchill have children?
Pamela Harriman and Randolph Churchill had one child: Winston Churchill.
How did Pamela Harriman and Randolph Churchill meet?
In 1939, while working at the Foreign Office in London doing French-to-English translations, Pamela Harriman met Randolph Churchill.
What did Randolph Churchill do?
Randolph Churchill joined his father's old regiment, the 4th Queen's Own Hussars, in August 1939.
Why did Pamela Harriman and Randolph Churchill marriage end?
Pamela Harriman filed for divorce in December 1945 on the grounds that he had deserted her for three years.

Question: When did this happen?
Self-contained rewrite: When did this Randolph Churchills absence happen?