UMNER-Class
Destroyer Minelayers
During the Solomons campaign in early 1943, the U.S.
Navy's ability to conduct high-speed, offensive mining operations was strained
by the shortage of destroyer minelayers (DMs). The few aging four-stack
destroyer minelayers were spread thinly and, because of the shortage,
destroyers were also being used for a variety of escort duties. Even so, mining
operations during the campaign were successful and encouraged navy planners to
consider converting some of the newer destroyer types, adding mine-laying
abilities.
Conversion studies for the BENSON (DD-421) class and
FLETCHER (DD-445) class were not impressive. Only ninety mines could be
accommodated on a FLETCHER conversion, just ten more that the old four-stackers
could carry. The BENSON class was even less promising. Design studies for an
ALLEN M. SUMNER-class (DD-692) conversion, however, indicated that up to 120
mines could be carried and in mid-1944, the Chief of Naval Operations
recommended that twelve SUMNERS then under construction to be completed as
light minelayers. Approval came on 20 July 1944 from Secretary of the Navy
James Forrestal and the conversion began.
Six (DD-735 through DD-740) were converted at Bath
Iron Works, Bath, Maine. They were renumbered as DM-23 through DM-28.
Three (DD-749, DD-750, and DD-751) were converted at
Bethlehem, Staten Island, New York. They were renumbered as DM 29, DM-30, and
DM-31.
Three (DD-771, DD-772, and DD-773) were converted at
Bethlehem, San Pedro, California). They were renumbered as DM 32, DM-33, and
DM-34.
The twelve ships that had traded torpedo tubes for
mine tracks formed divisions 7, 8, and 9 of Mine Squadron 3. The new DMs
entered the war too late to serve as minelayers, but the navy repeatedly called
on the guns of these ships in the final months leading to Japan's surrender.
These destroyer minelayers were designed to conduct
high-speed, offensive minelaying operations in addition to performing their
normal duties as destroyers. Because they kept almost all of their original
characteristics, they became hard-hitting and efficient fighting ships of the
Pacific Fleet.
Measurements
Length overall: 376'-6"
Extreme beam: 40'-10"
Displacement: 2,200 tons Standard
Armament
Three, twin 5-inch/38 caliber gun mounts
Two, quadruple 40-mm and two, twin 40-mm gun mounts
Eight, single 20-mm gun mounts and eight twin 20-mm gun mounts
Two depth charge release tracks (for 600 pound charges)
Four, single K-Gun depth charge throwers (for 300 pound charges)
Up to 120 mines, stored on mine tracks port and starboard on the main deck
Machinery
Four boilers
Two sets geared turbines
Two shafts/screws
Shaft horsepower: 60,000
Speed: 35 knots
Manning
Officers: 21
Enlisted: 342
As part of the conversion, tracks for handling the
mines were installed along both sides of the main deck extending from the
weather doors below the bridge to the stern. The mines were switched from port
to starboard on two cross tracks. The forward cross track was located in the
midships passageway, and the after track crossed just aft of 5-inch gun mount
No. 53. The cross tracks were connected to the main tracks by turntables that
completed the transfer of mines from one side of the ship to the other. The
main tracks rose gradually about three feet just aft of the stern crossover,
dropped sharply, and continued over the stern in a downward radius. The rise
controlled the overboard movement of the mines, and a large, double
steam-powered winch was located on the stern to hump the mines across the rise
in railroad car fashion.
The space and weight compensation for the
installation required the removal and relocation of a number of standard items
of destroyer equipment. Removal of both sets of torpedo tubes was the chief
solution to the weight problem. To make room for the humping winch, the single
20-mm mounts on the stern were removed, and the remaining single 20-mm guns
were replaced with a new twin mount. The depth charge tracks were retained, but
the ready service racks were landed. Two sets of depth charge projectors and
their ready service racks were also landed, and the four remaining sets were
relocated in the space left by the after torpedo tubes. Finally, the secondary
conning station was moved to the large open space between the stacks where the
forward torpedo tubes had been.
Some of the SUMNER DMs received improvements to
their antiaircraft battery because of the increase in kamikaze attacks during
the early months of 1945. A third quadruple 40-mm mount was added in the former
after torpedo tube position. The displaced depth charge projectors and ready
service racks were refitted on the main deck in a crowded arrangement between
the after deckhouse and gun mount No. 53.
Initial plans were for the converted SUMNER DMs to
have minesweeping as well as mine laying capabilities, and the GWIN (DM-33) was
fitted with minesweeping gear. By 1943, influence mines as well as contact-type
mines were in general use. As a result, the GWIN was equipped with a pulse
generator and pigtail cables for sweeping acoustic and magnetic mines in
addition to the normal contact sweep gear. As it turned out, the advantages of
this dual-capability could not override the extra cost of the gear's added
weight and no other DMs were so equipped.
The twelve DMs were completed between September and
October 1944. Their squadron was deployed with Rear Admiral Alexander Sharp's
Mine Flotilla, Task Group 52.2, led by the admiral's flagship, the TERROR
(CM-5). Most of Squadron 3 reached the Far East by February 1945 in time for
the Iwo Jima and Okinawa campaigns. Offensive mining was unnecessary at both
Iwo Jima and Okinawa, and the DMs were used primarily for fire support for the
GLEAVES-class (DD-423) destroyers that had been converted to destroyer
minesweepers (DMS). Organized in divisions of four or five DMS with one DM to
support the sweep operations, the units made fast sweeps outside the ten-fathom
line. The DMs also furnished covering fire for the smaller fleet minesweepers
and yard minesweepers that swept close in to the beaches and landing areas.
As kamikaze attacks increased during the Okinawa
campaign, many destroyers supporting fleet operations and on the picket line
were lost or severely damaged. Some were replaced with DMs from the mine force,
a number of which also were severely damaged.
Although never employed for their intended purpose
of offensive mine-laying operations, they were successful in their roles as
more conventional destroyers.
