On D-Day, did FDR violate the establishment clause?

President Franklin Delano Roosevelt delivered a radio prayer to the nation following the D-Day invasion of Normandy on June 6, 1944, which was released for newspaper publication to allow Americans to pray along. The prayer, written with help from his daughter Anna and her husband John Boettiger, addressed the uncertainty of the Allied invasion and called for divine assistance in liberating Europe from Nazi oppression.