[3e] USS Cairo

[Phaelen Bleux]

USS Cairo Ironclad Gunboat (1861, TL5)
Control of navigable waterways was critical during the American Civil War, and to this effect both the Union and the Confederacy began designing ships to gain control of them. By this point, wooden ships could no longer stand up to the power of the incendiary rounds being fired by the contemporary artillery, and had to be armored to withstand these rounds. The metallurgy of the day could produce sheets of iron up to 2" thick; these could be layered onto the sides of the ship to provide additional protection; typically 1-3 layers of iron were added. This iron was quite brittle, however, and in the case of the USS Cairo was backed by 2' of oak timber to help absorb the impact of the projectiles without shattering.

The USS Cairo was the first vessel of the City-class ironclads, produced in 1861. She was a paddlewheel-driven ship (some ironclads used screw propellers), and entered active service in 1862. She participated in actions against Fort Pillow (Tennessee), and against Confederate gunboats near Memphis. However, in December of 1862 she struck a mine (or torpedo, as they were often called at the time), becoming the first armored ship to be sunk in such a fashion. The ship sank in 12 minutes, with no hands lost.
The USS Cairo burns 7 cf of coal per hour of routine usage.

Subassemblies: Body with Mediocre lines +7.
Powertrain: 115-kW Forced-Draft Steam Engine with 115-kW Paddlewheel, 14 days of coal.
Occupancy: Up to 10 in cabins, up to 100 in hammocks. Assumes 251 crew.
Cargo: 0 cf

Armor: 3/10W overall
Side of Casemate: 5/180

Weaponry:
3x 66-pounder Smoothbore Cannons [Body:F] (100 shots each).
6x 42-pounder Rifled Cannons [Body:L,R,B] (100 shots each).
6x 32-pounder Rifled Cannons [Body:L,R,B] (100 shots each).
1x 4.4" Howitzer [Body:F] (100 shots).
Stats for all guns can be found on p. AN110.

Body: Navigation instruments, 1 luxury cabin, 4 cabins, 1 cabin with restraints (brig), 100 hammocks, galley, complete workshop, 3,514 man-days provisions, 4,800-lb. capstan, 4 external cradles for 4 longboats (p. SW114), primitive controls, 2,500 cf coal bunker.

Statistics:
Size: 175'x51'x?' Payload: 157 tons Lwt.: 512 tons
Volume: 51,200 cf. Maint.: 5 man-hours Price: $1,052,004

HT: 10. HPs: 24,819 Body.

wSpeed: 4.6 wAccel: 0.02 wDecel: 1 wMR: 0.05 wSR: 6
Draft: 6'. Flotation Rating: 1,459 tons.

Design Notes:
Structure is Heavy, with Standard materials. Waterproofed. Overall Armor is DR 10 Standard Wood. The volume of the armor is figured into the design, as per the rules on p. VEii5. Body volume was determined as displacement times 100 cf. Body volume as calculated using the Builder's Old Measurement was much higher (199,799 cf), probably because this ship is no longer all-wooden, so the value was abandoned. Accommodations are a guess, as are ammo loadouts. Design loaded weight was increased 1% to the historical. Design draft was 7.8'; the historical value is shown.

The upper hull superstructure is encased on 4 sides with sloping metal armor, 64mm thick. This gives a calculated DR of 180. Top save weight, a DR of 120 was purchased, with the additional DR being provided by the slope. To make the design easier, the armor is determined to cover the upper ½ of 4 sides of the body, or 1/3 the total body's surface area.

Sources listed the ship's top speed as 4.6 mph, 7 mph, and 9 mph. The initial output of the engine was reverse-engineered from the first speed and displacement weight. Increasing the ship's speed to 9 mph would require a 857-kW steam engine and paddlewheel, with a coal consumption of 51 cf per hour. Since this would necessitate a complete rebuild of what I had already done, I went with the lower top speed. The lower speed was also consistent with data I found for other ironclads of the period. The speed of the Mississippi River varies from 1-3 mph, so the ship can successfully navigate up and down river as designed.
Historical construction cost of the USS Cairo was $101,808.

Variants:
Her sister ships were the USS St Louis (sunk 1863), USS Cincinnati (sunk 1866), USS Carondelet, USS Mound City, USS Louisville, and USS Pittsburg. The latter four ships were sold after the war; the Carondelet and Mound City were scrapped; the Pittsburg was abandoned in 1870.

The above ordnance for the USS Cairo was as she was in January 1862. By November, her gun compliment had changed to 3 8" (66-pdr) smoothbores, 3 42-pdr rifled cannons, 6 32-pdr rifled cannons, 1 30-pdr rifled cannon, and 1 4.4" howitzer. As a side note, her rifled guns had actually been produced as smoothbore guns, and were rifled post-manufacture. This made them much more susceptible to rupture, and should lower Malf by 1 and increase range by 30% from the stats listed in Age of Napoleon.