Guns of the Cairo
The USS Cairo and her six sister gunboats were built to support the Union objective of wresting control of the Mississippi River from the Confederates. Her powerful guns, could interrupt Confederate commerce, batter opposing fortifications, repel enemy gunboats and rout any infantry or horse-drawn artillery.

Manning the Guns
When firing the Cairo guns, the gun crews performed precisely orchestrated movements.  Each man had his own duties. Safety and speed were of utmost importance.  Safety, because a prematurely discharged round or a bursting gun could cause more damage than a direct enemy hit. Speed, because the primitive sights and less-than-accurate guns made heavy volume of fire more important than careful aiming. All of the cannons on the Cairo are now on reproduction carriages. The thirteen original carriages have been removed from the outdoor gunboat exhibit. One original carriage has been placed on exhibit inside the Cairo Museum.

Cairo Stores
Cairo carried coal, shot, shell, powder, and supplies stored in compartments in the hold below the gun deck. When Cairo sank, the men saved only what they carried.  The storerooms yielded a wealth of artifacts, including many sailors’ personal possessions stored there for safekeeping. 

Chimneys
The chimneys vented smoke from the fire boxes and hot gases from the boilers.  The draft created by the chimneys made the coal fires burn hotter. Guy wires supported the chimneys and spreader bars held them apart.  A heat-shielding jacket prevented the hot chimneys from setting the boat on fire. The chimneys were also used for identification.  The seven City Class gunboats looked so much alike that different color bands were painted on the chimneys to tell the boats apart.  Cairo had gray bands. After Cairo sank, sailors knocked down the chimneys to hide the gunboat’s location.  The lower chimneys were not recovered.  These chimneys are the “ghosted” reproductions.

Steam Drum
The steam drum collected steam from the boilers and served as a manifold in distributing the steam to the engines, the capstan, the pumps, and the auxiliary engine.  It also prevented water from the boilers from passing through the engine.

Boilers
Steam, generated in the boilers, powered the engines which turned the paddle wheel. These iron boilers were built to hold tons of water and steam under pressure.  Boiler explosions did occur, often enough to give the commercial western steamboat a poor reputation for safety. The fire room was a hot, stifling place to shovel coal for hours on end.  Because a steamboat without steam could not move and was helpless if attacked, the gunboats kept fires burning, and steam pressure built up even when they were anchored. Coal, burned in the fire boxes, created hot gases which circulated by flues through the boilers.  The water turned to steam and passed through the steam drum to the engines, the hot gases vented through the chimneys.

Boilers
Type:                                       Return flue
Number:                                   5
Size:                                        36” diameter x 24’ long
Fuel:                                        Coal
Pressure:                                 140 lbs. sq. in.
Fuel consumption per hour:     18 to 20 bushels, 1980 lbs.

Hog Chains
Hogging is the term used to describe the tendency of the ends of the boat to droop and the center to hump up like a hog’s back. Hogging occurred under the stresses of the boat’s loads and movements because the river steamboats were extremely long in proportion to their depth.  They were also flat-bottomed, with no deep beam to give them longitudinal structural stability. A system of hog chains and braces prevented hogging.  The hog chains, iron rods 1-2½” thick, kept the bow and the stern from dropping; the thick, wooden braces kept the midships from raising.

Hammocks
With a crew of 175 men on board, only the officers and mates had sleeping quarters.  Enlisted men slept in hammocks on the gun deck and under awnings on the hurricane deck when the weather was good.  Hammocks were stored under canvas covers on the hurricane deck.  The berths gave extra protection to the hurricane deck during an engagement.  At times the hammocks were wrapped around the pilothouse to protect it during a fight.

Capstan
The capstan was a steam-driven winch used for pulling in the anchor, moving guns on the gun deck, and hauling lines.  The capstan could also be turned manually. The capstan moved weights of several tons and was braced by the capstan block attached to the keel.

Pilothouse
The pilothouse was the nerve center of the gunboat.  From the pilothouse, the pilot read the river and guided the gunboat through the shifting, often treacherous, river channels.  The commander, too, often occupied the pilothouse.  They communicated with the engine room through a signal board or by shouting through a speaking tube.  Pilothouses on Cairo and the six other City Class ironclads were dangerously exposed to enemy fire.

Hatch to the Coal Bunker
Coal for firing the boilers was stored in the bunker below and in large bunkers on both sides of the boiler hold. Coal heavers shoveled the coal to the firerooms, where it was fed into the firebox of the boilers. When underway, Cairo burned nearly a ton of coal an hour. 

Galley
On this galley stove the cooks prepared food for Cairo officers and men. Named the “Southern Belle,” the cast iron range was manufactured by S.S. Burton and Company of Cincinnati, Ohio. The sailors ate in messes of about 13 men, usually dining on salt beef or pork, the standard Navy fare. 

Armor
Cairo and the City Class ironclads were protected by 2½” thick armor plates mounted on laminated oak 12½ - 25” thick.  These gunboats were forward fighting vessels; they were designed to fight bows on.  With their heavily armored forward casemates, they could be only slightly damaged by a straight-on shot from an opposing gunboat or river battery.  Armor protected the boilers and engines on the starboard and port beams.  Cairo port and starboard quarters were reinforced with iron railroad rails.

The ironclads were not invulnerable.  To armor the entire vessel was impossible; the gunboat would have become too heavy to float.  The wooden decks could be crushed by plunging fire from an elevated battery.  The upperworks, chimneys, wheelhouse, and unarmored casemate sections could be damaged by enemy shot and shells.  Since much of the hull was unarmored below the water line, the boats could be sunk by a well-placed shot, a collision with a Confederate ram, or, as Cairo proved, by the newly developed torpedo (mine).

Thickness of plate armor:     2½”
Designed weight of plate armor:     75 tons
Weight of plate armor added by changes: 122 tons
Plate armor material:     charcoal iron
Armor plate sizes:     13” wide x 2’5 to 8’ ½” long
Wood backing for armor on five sides and back panels of pilothouse: 12”
Casemate side inclination:     45º
Casemate end inclination:     45º
Thickness of casemate timbres and sheathing:     25” forward, 12½” port starboard and aft    
Location of plate armor:     forward casemate and side casemates athwart engine machinery and pilothouse          
Railroad iron armor:     3½” iron rails from the forward-most side gun port to the front casemate both port and starboard
Iron armor provided a hard, protective shield; and wooden backing had flexibility which prevented the iron from shattering.  Tests by the U.S. Navy shortly before the Civil War proved that only the two materials combined were effective.

Ship’s Boats
Cairo carried three cutters and a launch.  Except when the ironclad was underway, these boats ferried men and supplies between the boat and shore and to other boats. These boats took armed parties of sailors up the rivers and creeks too shallow to float the gunboat.  They also became lifeboats the day Cairo foundered.

The Rudders
The rudders steered the gunboat.  They were controlled by steering cables attached to the wheel in the pilothouse.  A gunboat would be disabled if a shell cut the steering cables. Long pins called gudgeons attached the rudders to pintels on the rudder posts.  If damaged, the rudder could easily be removed for repairs.

Paddle Wheel
Cairo paddle wheel propelled the gunboat at a speed of 6 knots.  The paddle wheel was placed within the raceway between the casemates to protect it from enemy cannon fire. This paddle wheel is a recessed wheel similar to the well-known stern wheel.  The buckets were probably made of uniform-width wood and could have been easily replaced when damaged.

Paddle Wheel
4 paddle-wheel spiders made of iron arms and circles
Diameter:     22’
Deck Opening:     28’ x 18’
Driven by cranks mounted at either end at 90º to each other
Balanced opposite cranks by doubling the thickness of the bucket planks

Officers’ Quarters
The officers ate and slept separately from the enlisted men. The officers’ quarters were on the gun deck port and starboard of the paddle wheel.  In this location they escaped the heat of the fire room and the boilers. The captain’s quarters were directly aft of the paddle wheel. 

Wheelhouse
The protective casing around the paddle wheel was called the wheelhouse.  This unarmored structure was particularly vulnerable to plunging cannon fire. The head (latrine), containing a shower head and commode, was in a small building attached to the port side of the wheelhouse.  Water from the paddle wheel fed the shower and washed away the waste.

Engines
Steam engines powered the machines of the 19th century, and steam engines propelled the ironclad gunboats. Steam produced in the boilers was concentrated in the steam drum and passed through a throttle to drive the pistons of the engine.  A connecting pitman arm turned the crank of the paddle wheel.

The Engines
Type:                            Reciprocating steam -- noncondensing
Number:                       2
Cylinders:                     1 per engine
Cylinder inclination:    15º
Piston rods:                   4” diameter x 110’ long    

Ghosting
The light-colored laminate wood framing represents the “ghost” of Cairo structure that has not survived. Other structures ghosted on the Cairo hurricane deck include the center ridge beam and stanchions which supported the canvas awnings shading the hurricane deck.