Battery AMTB - Marrowstone Point

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Battery AMTB - Marrowstone Point (1944-1946) - Battery AMTB - Marrowstone Point was a reinforced concrete World War II rapid fire 90mm gun battery on Fort Flagler, Jefferson County, Washington. Battery construction started on 8 Oct 1943, was completed on 20 Dec 1943, and transferred to the Coast Artillery for use on 25 Mar 1944. Deactivated in 1946. Known within Puget Sound Harbor Defense as Battery AMTB 5.

Battery AMTB Marrowstone Point Emplacement #1
Battery AMTB Marrowstone Point Emplacement #2
Battery AMTB Marrowstone Point Emplacement #1
Battery AMTB Marrowstone Point Emplacement #2 from below

World War II (1941-1945)

Part of the Harbor Defense of Puget Sound.

The AMTB battery at Marrowstone Point consisted of two 90mm guns mounted on 90mm M3 gun mounts and two 90mm guns on M1A1 mobile carriages. 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 - Marrowstone Point Armament (edit list)
Model Serial
Manufacturer Carriage Service
1 90mm Rifle 186.15" M1 6682 General Motors Pedestal Mount, M3, #81, Fisher 1944-1946
2 90mm Rifle 186.15" M1 5389 Watervliet Pedestal Mount, M3, #166, Fisher 1944-1946
Source: RCW Form 1, 25 Mar 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 - Marrowstone Point Plan

Current Status

A part of Fort Flagler State Park, Jefferson County, Washington. No guns or mounts in place.

Location: Marrowstone Point, Fort Flagler, Jefferson County, Washington.

Maps & Images

Lat: 48.1012984 Long: -122.6873034

  • Multi Maps from ACME
  • Maps from Bing
  • Maps from Google
  • Elevation: 13.8'

GPS Locations:

See Also:


  • U.S.Army, Supplement to the Harbor Defense Project, Harbor Defenses of Puget Sound, (CCA-AN-PS), 12 Aug 1945, CDSG
  • Seacoast Artillery Ammunition Report of Harbor Defenses of Puget Sound For the period 1 July 1945 to 31 Dec 1945, NARA RG165, E257 Box 68 - Bolling Smith.


Fortification ID:

  • WA0031 - Battery AMTB - Marrowstone Point

Visited: 17 Aug 2022, 17 April 2010

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