In 1944, the Morale Operations Branch of the Office of Strategic Services (OSS) initiated the Musak project, musical propaganda broadcasts designed to demoralize enemy soldiers. Dietrich, the only performer who was made aware that her recordings would be for OSS use, recorded a number of songs in German for the project, including "Lili Marleen", a favorite of soldiers on both sides of the conflict. Major General William J. Donovan, head of the OSS, wrote to Dietrich, "I am personally deeply grateful for your generosity in making these recordings for us."