August 9, 1944 in an action off the Isle of Jersey boats of Motor Torpedo Boat Squadron 34 located and attacked several German minesweepers. First located by USS PT-508 and USS PT-509, USS PT-500, USS PT-503 and USS PT-507 were called into the area and they mounted an attack against the Germans. With torpedoes and guns firing the PT-509 became the only casualty when she collided with one of the German ships. The boat became lodged in the German vessel, which had some 100 troops on board who reportedly fired on the PT crew with small arms and even tossed hand grenades at them.

Of the crew of fifteen, there was only one survivor, Radarman 3rd Class John L. Page, who had a broken arm and was hauled aboard the German ship by her crew. He was taken prisoner and and treated in a hospital in France.

The PT-509 burned and reportedly exploded, the only remains were a small portion of her bottom found floating in the channel the next day.