Topsfield AFS
The Topsfield Gap Filler Annex is located on top of Musquash Mountain in Topsfield, ME
During the fifties and sixties, several Aircraft Control & Warning (AC&W) "gap filler" sites were constructed along the borders of the United States and across many of the "lower 48" states and Canada. These sites filled in the low altitude gaps between the long-range radar stations.
Sites built before 1958 would have been part of a manual radar defense network. After 1958, new sites would have been a part of the Semi-Automatic Ground Environment (SAGE) radar network and existing sites would have been upgraded. The last gap filler site in Maine was closed in 1968 and their phase-out continued across the country until approximately 1970. Topsfield was one of two gap filler sites associated with Charleston AFS in Charleston, ME, which is now a youth correctional facility. The other gap filler site was Sedgwick. Topsfield was activated at the end of 1958 and was inactivated at the end of 1967.
The SAGE continental air defense system was developed by the Massachusetts Institute of Technology's (MIT) Digital Computer Lab, the Air Force Cambridge Research Lab and MIT's Lincoln Lab between 1950 and 1957. SAGE was intended to identify and track Soviet bombers coming over the north pole. By the early 1960's, there were 23 SAGE "block houses" at various Air Force stations across the country. Each block house was a hardened, windowless structure that was home to an enormous 200+ ton computer. Each computer would speak to the other SAGE computers, ground radar, ship-board radar, and weather stations in order to keep tabs on legit air traffic and keep a constant eye out for Soviet traffic. The Ground to Air Transmitter/Receiver sites were used for communication between these fellow SAGE sites.
To reach the Topsfield site from Bangor, take I-95 north to Lincoln. Get off at the Route 2/Route 6 exit and head east into town. Stay on Route 6 through Lee and Carroll and cross into Washington County. After you cross into Washington County, it's only a few quick miles to East Musquash Lake, which will be on your left. At the far east end of the lake, you should see Tower Road on your right. The old yellow Air Force gate should still be there and there are power lines running up along the road as well.
 Old GateThe old Air Force gate. I've seen these at a few sites, including the Bridgewater gap filler site. May 2009 |  Tower RoadLooking up Tower Road. May 2009 |  Gap Filler Annex BldgCorner of the old building. You can see louvers here to vent for the generators. Not much of the old blue paint left anymore. May 2009 |
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 Gap Filler Annex BldgInside the building. This space would have held radar equipment. It has the start of a pretty good skylight going in this picture. May 2009 |  Gap Filler Annex BldgBack side of the building. Here you can see the diesel fuel tank for the generators and the back door that leads to the generator room. May 2009 |  Tank and TowerA wider shot from the back of the building that shows the diesel tank and the tower. May 2009 |
 Diesel TankThe tank was removed during the summer of 2009 as a part of a clean-up project by the military. Sept 2009 |  Diesel TankAnother shot of the old diesel tank pads. You can see a newer cell phone tower in the background. Sept 2009 |  TowerAnother wide shot of the tower. Sept 2009 |
 Generator RoomInside the generator room. You can see the inside of the louvers for ventilation. May 2009 |  Vent HoodI found one of the vent hoods for the generator room in the woods. This would have gone over the louvers to provide some weather protection from driving rain, snow, etc. May 2009 |  Tower BaseOne of the four feet of the tower. Still very sturdy today. May 2009 |
 StairsThe bottom level of stairs was very unsteady with several bent/broken stairs and the risers themselves were no longer anchored. May 2009 |  Gap Filler Annex BldgLooking at the roof of the building, you can see the top side of the hole that has started. May 2009 |  Gap Filler Annex BldgAnother shot of the "skylight." Sept 2009 |
 ViewThe view from the tower is pretty spectacular. Sept 2009 |  ViewView from the tower, looking at some of the newer towers on the mountain. Sept 2009 |  ViewSept 2009 |
 Vintage ImageA vintage image from the 60's, courtesy of Bill Rayfield. Looking down from the tower at the Dodge crew cab they used to drive up the mountain. |  Vintage ImageA vintage image from the 60's, courtesy of Bill Rayfield. Looking up at the tower. |  Vintage ImageA vintage image from the 60's, courtesy of Bill Rayfield. Taken at the end of Tower Road. You can see the Z-65 identifier which makes it a part of the SAGE system, attached to Charleston AFS. Also visible is the fire tower sign. Many of the gap filler towers were also used as fire watch towers by the forest service. |
 Vintage ImageA vintage image from the 60's, courtesy of Bill Rayfield. Looking up at the radome. |