General Gun and Turret Information Pages
A drawing of the USS IOWA(BB-61)
A warship serves as a platform to carry its armament into combat.
It
exists for no other reason. As a type, the battleship was intended for offensive
operations against other battleships and was designed to carry the heaviest of guns.
Secondary and anti-aircraft guns were also provided as a defense against attacking
destroyers and aircraft. The armament of the USS IOWA is arguably the finest
ever conceived and produced. The guns, their mountings and operating machinery were
fashioned into a complex and sophisticated weapons system which after nearly half a
century, is still the finest of its type afloat.  The main armament of the IOWA is the 16in/45cal Mark 7 gun.
The IOWA class are
the only battleships to mount this weapon which is a considerable improvement over the
16in/45cal guns mounted in the North Carolina and South Dakota classes.
The Mark 7 gun fires two basic rounds, a 2,700 pound AP (Armor Piercing) and a 1,900
pound HC(High Capacity) shore bombardment projectile. Nine of these weapons are
mounted in three 3-gun turrets. They are designated 3-gun turrets, as opposed to
triple turrets because each gun is mounted ion an individual slide with its own elevation
drive. A triple turret has a single slide providing bearing surfaces for all three
guns and uses a common elevation drive. Two turrets are located forward and one aft
of the superstructure.
The gun is a lightweight, built-up type consisting of a liner, tube
jacket, hoops, locking rings, a liner locking ring and a yoke ring. Assembly is
accomplished by heating and expanding each piece before sliding it into position over the
tube. When the components cool and shrink, a tight single unit is formed.
The
liner is inserted from the breech end, while an electric shrink pit and its locking ring
prevents expansion aft when the gun is fired. The liner is rifled with ninety-six
grooves, 0.15in deep, with a uniform right-hand twist of one turn every twenty five
caliber's.
Each gun is mounted in an
individual slide with its own elevating gear. The gun assembly includes a breech
mechanism, firing lock, gas ejector and yoke. It is designed for removal from the
slide and gun port without dismantling the turret. The breech mechanism is a
rotating Welin interrupted screw plug and Smith-Asbury swinging carrier type.
The
screw box liner and breech plug are segmented with stepped screw threads arranged in
fifteen sectors of 24 degrees each. The first sector is blank followed by four
threaded sectors and this pattern is repeated three times for a total of twelve threaded
and three blank sectors. The breech plug is locked with a 24 degree rotation after
the plug threads are engaged. The firing lock receives a hand-inserted plug-like
brass cartridge about the size of a 30 cal carbine shell loaded with FFG black
powder. There is a provision for electric or percussion firing of the prier
when the breech is closed. When the breech is opened after firing the bore is
cleared automatically by a 175psi low-pressure air system from the gas ejector
system. The gun yoke is a large counterbalancing unit mounted on the gun shoulder
providing seats for the recoil cylinder piston rod and counter recoil cylinder yoke rods.
The nine gun assemblies are mounted in three turrets, all on the
centerline with arcs of train providing fire concentration of nine guns on either beam,
six guns forward and three guns aft. The three turret assemblies are very similar in
design and construction, the main difference being tin the depth of their
structures. Each consists of a gun house with rotating structure, a fixed structure,
a barbette, magazines and associated equipment.
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page in "General Information about the 16in. gun"
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All of the information in these pages is from the two sources below:
Reference #1
*Muir, Malcolm, THE IOWA CLASS BATTLESHIPS, 1987, Sterling Publishing, New
York. ISBN 0-7137-17327
Reference#2
*Sumrall, Robert, F., IOWA CLASS BATTLESHIPS, 1988, Naval Institute Press,
Annapolis. ISBN 0-87021-298-2
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