The 609th Coast Artillery (Antiaircraft) was one of a series of regiments constituted and organized in the Army of the United States (AUS) in November and December 1942.
The regiment was broken up in January 1943 and its former elements were reorganized and redesignated. The former 2d Battalion, 609th Coast Artillery, after a brief period as an independent coast artillery antiaircraft automatic weapons battalion, became 204th Antiaircraft Artillery Battalion (Automatic Weapons).
The battalion landed at Normandy 19 June 1944 (twelve days after the Normandy Invasion) as an element of Third Army and it's campaign credits include Normandy, Northern France, Rhineland, Ardennes-Alsace and Central Europe Campaigns.
I can provide a complete list of wartime assignments and attachments for a fee.