Battery AMTB - Gaffey Bulge

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Battery AMTB - Gaffey Bulge (1943-1946) - Battery AMTB - Gaffey Bulge was a reinforced concrete World War II 90mm gun battery on Fort MacArthur, Los Angeles County, California. AMTB stands for Anti Motor Torpedo Boat. Battery construction started Jun 1943, was completed Oct 1943 and transferred to the Coast Artillery for use 4 May 1944. Deactivated in 1946.

90mm AMTB Gun on M3 Mount, image courtesy Fort MacArthur Museum
Gaffey Bulge AMTB Mount Base #1

Battery AMTB - Gaffey Bulge History

Part of the Harbor Defense of Los Angeles.

Four Anti Motor Torpedo Boat (AMTB) batteries were built for the Harbor Defense of Los Angeles during World War II under Job No. FS-8 at a total cost of $76,576.03. All four batteries were constructed between June 1943 and October 1943 and all four were accepted for service on 4 May 1944.

Each of the four batteries consisted of two fixed gun emplacements of 90mm M1 guns on M3 pedestal mounts with a heavy shield. Additionally provisions were made for two temporary mobile gun positions at each of the four locations and each position had supporting structures for ammunition storage and a central power source. Two of the AMTB batteries were located on Fort MacArthur, (Battery AMTB - Navy Field & Battery AMTB - Gaffey Bulge) and the other two were located off the main reservation at Terminal Island (Battery AMTB - Terminal Island) and Bluff Park, Long Beach (Battery AMTB - Bluff Park).

The dual mission of these AMTB batteries was both to defend the harbor against smaller, faster naval vessels that might evade the larger batteries and to defend against aerial attack.

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 - Gaffey Bulge Armament (edit list)
Model Serial
Manufacturer Carriage Service
1 90mm Rifle 50 Cal M1 7046 General Motors Pedestal Mount, M3, #186, F B D 1943-1946
2 90mm Rifle 50 Cal M1 7271 General Motors Pedestal Mount, M3, #258, F B D 1943-1946
Source: RCW Part 1, 5 Dec 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
Battery AMTB - Gaffey Bulge Plan 5 Dec 1944

Current Status

No gun or mounts in place but the base of the mounts can still be seen. The Gaffey Bulge is a semicircular protrusion in Gaffey Street that allows Gaffey Street to go around a hill. Mount base #2 is covered with a circular platform that once contained a tourist telescope.

Location: Fort MacArthur, Gaffey Bulge, Los Angeles County, California

Maps & Images

Lat: 33.712495 Long: -118.291992


  • U.S.Army, Supplement to the Harbor Defense Project Harbor Defenses of Los Angeles, (LA-AN-WDC-44), 31 Aug 1944, CDSG


Visited: 31 Jan 2009

Battery AMTB - Gaffey Bulge Picture Gallery

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