In addition to the Civil Air Patrol (CAP), large U.S. Navy blimps assisted with coastal air patrol. Housed in giant hangars, they operated out of several locations on both coasts. The blimps flew hundreds of feet above the ocean's surface, looking for mines, survivors of torpedoed boats, and any suspicious bubbles or periscope wakes left by enemy submarines. Under good conditions they could spot the shadow of an enemy submarine up to 90 feet below the surface. The blimps would often carry several homing pigeons, birds that could fly messages back to the home station in case of emergencies or radio communications blackouts.