Battery AMTB 911

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Battery AMTB 911 (1943-1946) - Battery AMTB 911 was a reinforced concrete World War II AMTB rapid fire 90mm gun battery on Fort Terry, Plum Island, Suffolk County, New York. Battery construction started 18 May 1943 was completed on 28 Jun 1943 and transferred to the Coast Artillery for use 20 Dec 1943. Deactivated in 1946.

Battery AMTB 911 History

Part of the Harbor Defense of Long Island Sound.
The AMTB battery at Pine Point consisted of two 90mm guns mounted on 90mm M3 fixed gun mounts and two 90mm guns mounted on 90mm M1A1 mobile gun mounts. Concrete firing platforms were laid for both of the fixed guns. 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. Each weapon required a crew of 15, 9 men in the gun squad and 6 men in the ammunition squad. Ammunition was stored in igloo type magazines behind the batteries. Power was provided by two M-7 portable generator sets in revetments.

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)

Battery AMTB 911 Armament (edit list)
Model Serial
Manufacturer Carriage Service
F1 90mm Rifle 186.15" M1 6932 GM Pedestal Fixed Mount, M3, #117, GM 1943-1946
F2 90mm Rifle 186.15" M1 6699 GM Pedestal Fixed Mount, M3, #25, GM 1943-1946
M1 90mm Rifle 186.15" M1 ? Unknown Mobile Mount, M1A1, #?, Unknown 1943-1946
M2 90mm Rifle 186.15" M1 ? Unknown Mobile Mount, M1A1, #?, Unknown 1943-1946
Source: RCW Form 1, Aug 1944, Coast Defense Study Group, Berhow, Mark A. ed, American Seacoast Defenses: A Reference Guide, 2nd Edition, CDSG Press, McLean, VA, 2004, ISBN 0-9748167-0-1, pages 80-81, 206
Battery AMTB 911 Plan

Current Status

No period gun or mounts in place.

Location: Plum Island, Suffolk County, New York. Map point is approximate.

Maps & Images

Lat: 41.165236 Long: -72.198785


  • U.S.Army, Supplement to the Harbor Defense Project of Long Island Sound, (HDLIS-AN-45), 15 Feb 1945, CDSG


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