Battery AMTB - Gravelly Beach

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Battery AMTB - Gravelly Beach (1944-1946) - Battery AMTB - Gravelly Beach was a reinforced concrete World War II rapid fire 90mm gun battery on Fort Baker (1), Marin County, California. Battery construction started 29 Jun 1943, was completed 6 Sep 1943 and transferred to the Coast Artillery for use 18 Jan 1944 at a cost of $ 4,907.63. Deactivated in 1946.

Battery AMTB - Gravelly Beach Emplacement #2 from Above
Battery AMTB - Gravelly Beach Emplacement #2 Mounting Bolts
Battery AMTB - Gravelly Beach Emplacement #2 from the Beach

Battery AMTB - Gravelly Beach History

Part of the Harbor Defense of San Francisco.

The AMTB battery at Gravelly Beach consisted of two 90mm guns mounted on 90mm M3 fixed gun mounts and two 90mm guns on mobile M1A1 carriages. Concrete pads for both the fixed guns were constructed. 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.

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 - Gravelly Beach Armament (edit list)
Model Serial
Manufacturer Carriage Service
1 90mm Rifle 186.15" M1 6915 General Motors Pedestal Mount, M3, #100, Fisher 1944-1946
2 90mm Rifle 186.15" M1 6924 General Motors Pedestal Mount, M3, #109, Fisher 1944-1946
1. RCW Form 1, Oct 1943
3. 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, 217.
4. Armament Data - Harbor Defenses of San Francisco, undated, NARA RG165, E257 Box 68 - Bolling Smith.
Battery AMTB - Gravelly Beach Plan

Current Status

Part of the Golden Gate Recreation Area (GGNRA) administered by the National Park Service. No period guns or mounts in place. One concrete pad is exposed and the other is visible.

Location: Fort Baker, Marin County, California.

Maps & Images

Lat: 37.827144 Long: -122.489169



Visited: 20 Aug 2009

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