The gun fired two kinds of projectiles: the Mk 8 Armor Piercing (AP) round weighing 2,700 pounds and the Mk 13 High Capacity (HC) �?or high explosive �?that weighed 1,900 pounds.  A Mk 8 AP shell could penetrate 20 inches of armor or 21 feet of steel reinforced concrete at 20,000 yards.  The Mk 13 HC shell created a crater 50 feet in diameter by 20 feet deep; nine HC rounds would wipe out one square mile.  The projectiles were propelled to a maximum range of nearly 25 miles by a Service Charge of six 110 pound bags of powder (660 pounds total).  For firing on reverse slopes (like mortars and howitzers), a Reduced Charge of six 55 pound bags (330 pounds) was used.  Rate of fire was one round per gun every 30 seconds.  Every time the breech block was lowered to load a projectile and powder, high pressure air was injected into the gun chamber to remove toxic and explosive gun gas from the barrel through the muzzle.

How 16-inch shells on the projectile flat were moved to the shell hoists inside the turret.  (Photo: Iowa Veteran’s Association)

The loading sequence began when the breech block was opened.  High pressure air was injected into the chamber of the gun barrel to clear any gun gas or powder bag remnants.  The Plug Man wiped the face of the breech plug and made sure the bore was clear to receive the waiting projectile and powder bags.

Plug Man aboard USS MISSOURI (BB-63).  The brass tube above his shoulder a gas ejection nozzle.  The breech block was unlocked, lowered, raised, and locked by hydraulics.  (Photo: US Navy)

Once the breech plug was down, the Projectile Man operated the spanner tray.  The tray unfolded and the projectile was lowered to align with the breech before ramming.  The Rammer Man used a chain-link rammer to push the projectile into the breech of the gun.  Once the projectile was rammed, the rammer was retracted in preparation to loading the powder bags.  All these operations were overseen by the Gun Captain who was responsible for safe operation of his gun.

A 16-inch HC projectile in its hoist tube as the spanner tray unfolds for loading.  The arm-length “glove�?on the Plug Man is used to clean the face of the breech plug.  The flame and blast door for the powder hoist is just to the left of the projectile nose.  Note that the protective fuze cap has been removed before the projectile is rammed.  (Photo: Iowa Veteran’s Association)

After the rammer retracted, the Powder Man opened the door to allow three 110-pound powder bags to roll onto the spanner tray.  The door was then closed, the powder car moved one flight, and the rammer extended to push the three bags into the breech.  The rammer then retracted, the powder door was opened again, and three more bags were put on the spanner tray.  The powder hoist door was closed, the hoist returned back to the powder handling room, and the rammer extended to ram the second batch of three bags into the breech.

Powder hoist door open and powder bags being positioned on the spanner tray prior to ramming.  (Photo: Iowa Veteran’s Association)

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Powder hoist door is closed and the three powder bags are ready to ram into the breech.  Note the red ends of the powder bags.  This is the initiator pad that contains black powder to ignite the smokeless powder in the silk bags.  These bags are consumed when the gun fires.  (Photo: Iowa Veteran’s Association)

After the last powder bag was rammed into the chamber of the gun, the rammer was retracted.  The spanner tray was refolded and the end of the hoist raised to receive another projectile.  The Plug Man raised the breech block, it rotated into firing position, the Plug Man removed a primer from is cartridge belt and inserted the primer into the firing lock of the breech block.  The gun was ready to fire and elevated to match the gun orders from the director.  Firing was accomplished electrically.  In case the electricity failed, the primer could be fired by mechanically.

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A Mk 7 gun breech plug in its closed and locked position.  The firing lock is in the center of the breech plug.  The breech plug is lowered, raised, and locked by hydraulics.  Note the powder hoist door is on the right for this gun and the fire suppression system nozzle at the top of the photo.  (Photo: Iowa Veteran’s Association)

The Mk 7 guns were always fired from off-centerline of the ship.  Each gun could fire independently or in salvo of three guns or a broadside of nine guns.  When fired in salvo, guns No. 1 and No. 3 fired together while gun No. 2 fired 0.2 second behind the other two.  This prevented a collision between the in-flight projectiles.  At maximum ranges, the time-of-flight for a projectile was about 1-1/2 minutes.  Muzzle velocity of the AP projectile was 2,300 feet per second and 2,635 feet per second for the HC projectile.

Gun 2 of No. 2 turret firing.  Note the expanding gas cloud of burning propellant.  The American flag on top of turret No. 1 is an air recognition sign.  Barrels 1 and 2 of turret No. 1 are ready to fire, while barrel 3 is lowered to the loading position.  (Photo: Iowa Veteran’s Association)

There are several anecdotes that illustrate the power of the Mk 7 16-inch/50 caliber gun.  In one case, Quartermaster friend of mine told me that when the USS NEW JERSEY was on the gun line off Vietnam, they had to update the charts after every fire mission.  The guns of the ship actually “rearranged�?the countryside to the extent that the area charts were affected.

(Go to Part 2 of 2)

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