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Coast Artillery Mine Planter Device
The Army Mine Planter Service was authorized this insignia with a mine case below the insignia by War Department Circular 25, dated 17 January 1920.

Operated by: 
Battery A 21st Coast Artillery
Battery B 21st Coast Artillery

Mine Planter Sylvester12th Coast Artillery Mine Planter (CAMP) Battery
Mine Planter Frank:  19th Coast Artillery Mine Planter (CAMP) Battery 

Support Structures:
Mine Casemate
Fire Control Tower #7

Page Contents

Related Documents

The M3 Buoyant Mine
The M4 Ground Mine
Army Mine Planters
Shore Facilities
Mine Field Protection
RCW - Mine Plotting Room
Location of Elements
Map of Facilities
M4 Mine Configuration


The original mine defenses of Fort Miles were M3 floating contact mines.  These mines were tethered to an anchor placed on the bottom of the bay.   In 1943 these mines were replaced by M4 ground mines, which sat on the bottom of the bay.  They were much larger, and far more powerful than their M3 predecessors.  Mines were not contact controlled, meaning they did not detonate upon impact with a vessel.  Mines were detonated by an electrical charge of 500 volts, sent from a mine control room which was located in the mine casemate.  Visual identification of targets was done by spotters in Fire Control Tower #7.  The advantage to having a mine controlled by an operator instead of simply detonating upon contact was that the harbor entrances and shipping channels could be mined safely without friendly vessels being accidentally sunk by friendly fire.  It also meant that in the event of a naval attack by an enemy, mines could lay dormant during enemy mine sweeping operations, and then be detonated when a major target was within range.  The mines worked by creating a pressure wave upon detonation which would break the keel of a nearby ship.
The M3 Buoyant Mine

The M3 buoyant mine was anchored to the floor of the bay by a 2000 pound weight and moored by a steel cable.  The mine itself would float just beneath the surface of the water.  The mine measured approximately 2 to 3 feet in diameter and carried a 500 pound TNT charge.  These were typically set in groups of 19, and spanned 1800 feet of water.  The M3 mines could register a contact, and did so by using a device similar to the tilting device on a pinball machine.  It required a severe jolt to move a ball sufficiently to allow the mine to arm and signal the casemate that it had been contacted.

When the M3 mine field was removed in 1943, many of the now deactivated devices found new life around Fort Miles as lawn ornaments, as seen in the photograph to the right.  The mine depicted on the coast artillery mine planter insignia above represents an M3 mine.

A soldier at Fort Miles leans against a deactivated M3 mine used as decoration on post.
Photo Source:  Fort Miles Archives

The M4 Ground Mine

The M4 ground mine was placed directly on the floor of the bay and was marked by a buoy that would be removed after the field was planted.  The M4 mine field was planted in 1943 and the devices were much larger, carrying a 3000 pound TNT charge.  They were detonated in a similar fashion to the M3, in that they would receive a signal from a controller in the mine casemate that would detonate the mine.  The M4 featured additional advantages, as the devices were completely out of the way of friendly shipping activities and were of a much better design than the previous M3, making them much safer and more reliable.  Due to the higher yield of the M4 mine, they were set in groups of 13, with a total of 35 groups placed in the Delaware Bay.  This made the total mine count 455, making the Delaware Bay one of the most heavily mined bay entrances in the country, second only to the Chesapeake. 

This deactivated M4 mine was once planted on the floor of the Delaware Bay at Fort Miles.
Photo Credit:  Michael Rogers

Army Mine Planters

Army mine planting vessels were tasked with planting and maintaining the mine field at Fort Miles.  As of 1 July 1945, the submarine mine flotilla consisted of the following:

Type Name Length Beam Draft
USAMP Frank 188 ft 37.75 ft 12 ft
USAMP Sylvester 188 ft 37.75 ft 12 ft
DB L-71 64 ft 18 ft 6 ft
DB L-72 64 ft 18 ft 6 ft
DB L-77 64 ft 18 ft 6 ft
DB L-109 64 ft 18 ft 6 ft
Mine Yawls M-312, M-313, M-314, M-353, M-354, M-355, M-381, M-382, M-391, M-411, M-412
USAMP United States Army Mine Planter
DB Distribution Box Boat


USAMP-12 "Frank" docked at Fort Miles.  This vessel was identical to the USAMP "Sylvester" which was also stationed at Fort Miles.
Photo Source:  Fort Miles Archives

Shore Facilities
Wharves, Channels and Turning Basins
The wharf was originally 24 ft x 1800 ft.  The addition of a 200 ft wing at the end of the wharf was approved by letter 11 March 1943, subject "Additional Docking and Boat House Facilities, Ft. Miles, Del."  No channel or turning basins were necessary.

Boat House and Small Boat Basins Capacity
There was a boat house at the end of the wharf for 12 mine yawls.  The boathouse was destroyed by fire after the war.

Loading Rooms
Two 38 ft x 48 ft loading rooms were located at the base of the mine wharf.  They no longer exist today.

Mine Storehouse
One 103 ft x 207 ft mine store house was constructed for storage and protected working space.  The structure still exists, and is currently used by the University of Delaware.

Explosive Storage Magazines
Two magazines 10 ft x 10 ft were built adjacent to the loading rooms.  These were used to store explosive charges that were to be loaded into the mines prior to planting.  These structures still exist today.

Mine Casemate
The bombproof concrete casemate consists of a plotting room 22 ft x 22 ft, an operations room 22 ft x 22 ft, converter room 14 ft x 17 ft, and latrines.  Space and facilities were sufficient to provide for the mine battalion command post.  All mine operations were controlled from this casemate, as well as the detonation of the mines themselves.  The structure still exists today.  Click here for more information on the mine casemate.

Cable Huts
Six cable huts were used as terminal stations for the cables that connected the mines to the controllers on shore.  All of the cable huts are still extant at Cape Henlopen.

Mine Plotting Room
The mine plotting room (PLR) is located inside of the mine casemate.  Spotters in FCT#7 send information on the location of vessels in the minefield via telephone to personnel in the mine plotting room.  The location of each mine is precisely plotted on a board in this room, and operators can determine which mine in which group will most effectively sink a target vessel depending on its location in the minefield.

Mine Battalion Command Station
The battalion command station oversees all operations of the mine planting battalion at Fort Miles.  It was headquartered in the bombproof mine casemate.

Mine Field Protection

Protection of the minefield was afforded by artillery and searchlights on shore.  The following batteries were assigned surface protection duties of the minefield at Fort Miles.

Artillery Batteries Searchlight Batteries
Battery 5
Battery 5A
Battery 5B

Battery Hunter
Battery Herring
Searchlight Battery 7
Searchlight Battery 8
Searchlight Battery 9
Searchlight Battery 10

Mine Yawl Boat House at Fort Miles.
Source:  Fort Miles Archives

T-403 Mine Storage Building.
Currently used by the University of DE.
Photo Credit:  Michael Rogers

Interior of T-431 Explosive Storage Magazine.
Both magazines are still standing, but have been overgrown with brush.
Photo Credit:  Michael Rogers


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