The most impressive feature of the former Montauk Air Force Station is the enormous surveillance radar which was abandoned in place by the Air Force in 1981. This extremely powerful radar could detect airborne objects at distances of well over 200 miles. The huge antenna of the AN/FPS-35 radar weighs roughly 75 tons. This is the sole remaining example of the large "frequency diversity" radars which were deployed at select sites across the United States during the Cold War.
Abandoned, Military - Communications
Former military R&D location associated with alleged WWII invisibility research (the Philadelphia Experiment) and other activities. Major focus for "technological cover-up" conspiracy theorists. Many radar facilities remain on site, though the majority of the former Camp Hero is now a park.
Links: www.fortunecity.com, cryptome.org