The defunct U. S. Army post Fort Hancock at the north end of the peninsula is open to visitation by the National Park Service. The Sandy Hook Proving Ground was used by for many years—beginning after the Civil War until 1919, when the facility was moved to Aberdeen, Maryland—and was later the site of a Nike missile defense installation. The Sandy Hook Nike station is one of a very few stations that are still intact. Almost all of the fort's gun batteries are closed to the public due to their hazardous condition. The exceptions to this are Battery Potter and Battery Gunnison. Battery Potter is open frequently for tours on the weekends, as well as Battery Gunnison which is being restored by volunteers and has two six-inch (152 mm) M1900 guns installed; the weapons were placed there in 1976. Guided tours show visitors a Nike missile, the missile firing platforms, and a radar station with 1960s-era computers. A Civil War-era 20-inch Rodman gun is also in the park; this was an experimental gun that was the largest type produced by either side of that war.