Battery AMTB 942

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Battery AMTB 942 (1943-1946) - Battery AMTB 942 was a reinforced concrete World War II AMTB rapid fire 90mm gun battery on Great Brewster Island Military Reservation, Suffolk County, Massachusetts. Battery construction started in 1943, was completed in 1943 and transferred to the Coast Artillery for use in 1943. Deactivated in 1946.

World War II

Part of the Harbor Defense of Boston, Massachusetts.

The AMTB battery at Great Brewster Island consisted of two 90mm guns mounted on 90mm M3 fixed gun mounts, two 90mm guns mounted on 90mm M1A1 mobile gun mounts and two 37mm guns on mobile mounts. Concrete pads were provided for both fixed guns and often wooden gun platforms were provided for the mobile guns. A single earth covered magazine provided protection for the ammunition. Electric power was provided by M-7 portable generators.

The battery had a dual mission of defense against fast enemy motor torpedo boats and enemy aircraft. The effective range of the guns was about 8,000 yards or 4.5 miles. Each weapon required a crew of 15, 9 men in the gun squad and 6 men in the ammunition squad.

AMTB Front View
AMTB Interior View
AMTB Side View
AMTB Back View

The above photos were taken at Fort Monroe, Battery Parrott

From FM 4-91: "This weapon consists of the 90-mm gun M1 and top carriage M1A1 on the 90-mm gun mount M3. The mount M3 is of the turret type, the shielding being constructed of boiler plates. This boiler plate shield provide fragmentation protection only. No shielding is provided at the rear due to the requirements for service of the piece. A sighting port in the shielding in front permits sighting in direction by the gun pointer."


  • FM 4-91 - 90-MM Gun, Fixed Mount Service of the Piece
  • FM 4-126 - Antiaircraft Artillery, Service of the Piece, 90-mm Antiaircraft Gun
  • TM 9-373 - 90-mm Gun M1 and 90-mm Gun Mount T3 (M3)

Current Status

Part of Boston Harbor Islands National Recreation Area and Boston Harbor Islands State Park, Suffolk County, Massachusetts. No period gun or mounts in place.

Location: Great Brewster Island, Suffolk County, Massachusetts

Maps & Images

Lat: 42.33381 Long: -70.89578

  • Multi Maps from ACME
  • Maps from Bing
  • Maps from Google
  • Elevation: .....'


  • U.S. Army Corps of Engineers, FUDS Archives Search Report, Findings for the former Great Brewster Island Military Reservation AMTB 942, Project No. D01MA048102, December 1997. Large PDF Download
  • U.S.Army, Supplement to the Harbor Defense Project of Boston, Massachusetts, (HDB-AN-45), 31 Jan 1945, CDSG


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