During World war II, the U.S. Army set up an Air Warning Station (Martha`s Vineyard AWS-6) at what would later become the U.S. Air Force`s Chilmark Gap Filler radar site, site P-45B / P-10E. The Signal Corps set up a skeletal tower which was originally said to be used for signals associated with Coastal Artillery batteries in the region. After the war, a local paper reported that residents only then learned that the array atop the tower was in fact a radar set.

The site also included barracks and "machine gun nests," the latter presumably being provided for site protection, including what must have been a rather valuable and classified radar system at that time.

The Army radar site (later the Gap Filler radar site) was located atop "Peaked Hill," in Chilmark. This same GFA site reportedly was utilized by MITRE as part of the Experimental SAGE Sector (ESS) in the mid 1950`s, before being transferred to the U.S. Air Force.

The former Army base was quite small, on the order of 4 acres or so in its original form. Later, it seems to have been reduced to about 1.5 acres, as the security perimeter (presumably including the machine gun facilities) were no longer required. The last remaining Army buildings were demolished during 1977, according to one source. The GFA building, according to aerial imagery, apparently was still extant as of 1995 -- though it is not known at this time if that building is still standing today.