what does dd stand for in the navy
Hull classification symbol It is important to understand that hull number letter prefixes are not acronyms, and should not be carelessly treated as abbreviations of ship type classifications. Thus, "DD" does not stand for anything more than "Destroyer". "SS" simply means "Submarine". And "FF" is the post-1975 type code for "Frigate."[6]
D-Day (military term) The earliest use of these terms by the United States Army that the U.S. Army Center of Military History has been able to find was during World War I.[3] In Field Order Number 9, First Army, American Expeditionary Forces, dated 7 September 1918: "The First Army will attack at H hour on D day with the object of forcing the evacuation of the St. Mihiel Salient."