Overview
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.
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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.
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A soldier at Fort Miles
leans against a deactivated
M3 mine used as decoration
on post.
Photo Source: Fort
Miles Archives |
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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.
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This deactivated M4 mine was
once planted on the floor of
the Delaware Bay at Fort
Miles.
Photo Credit: Michael
Rogers |
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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 |
|
Legend: |
|
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 |
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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.
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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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