Operation Mincemeat is a West End musical comedy, now on Broadway, about one of the stranger true stories of the second world war, where a corpse was sent ashore in Spain to divert the German Army from Sicily.
In the second act, one of the characters is asked to help build the back story of the fake persona of the corpse, and wrote him a letter. And so, channelling her love for her fiance who died in the Great War, she spills out her heart in "Dear Bill".
This is the composer performing it at Studio 54 in NYC.