Casco-class monitor

USS Casco on the James River, 1865
Class overview
Name:	Casco-class light draft monitor
Builders:	Various
Operators:	United States Navy
Preceded by:	Passaic-class
Completed:	20
Retired:	20
General characteristics
Displacement:	1,175 tons
Length:	225 ft (69 m)
Beam:	45 ft (14 m)
Draught:	6 ft (1.8 m) (designed)
Propulsion:	Steam engine, twin screws
Speed:	8 knots (15 km/h; 9.2 mph) (designed)
Armament:	2 × 11-inch (280 mm) guns

The Casco-class monitor was a unique class of light draft monitor built on behalf of the United States Navy for the Mississippi theatre during the American Civil War. The largest and most ambitious ironclad program of the war, the project was dogged by delays caused by bureaucratic meddling. Twenty ships of the class were eventually built at great expense, but proved so unseaworthy when trialed that they were quickly sidelined, causing a public scandal.

After the success of the US Navy's first monitor, USS Monitor, in preventing the Confederate ironclad CSS Virginia from breaking the Union blockade at Hampton Roads in the spring of 1862, the navy became enthused with the monitor concept (at the expense of the larger broadside ironclad type), and ordered a number of new classes of monitor, one of which was the Casco class. The Cascos were a unique "light draft" class designed specifically for operating in the shallow bays, rivers, and inlets of the Confederacy.

The specifications for the Casco class originally called for a vessel with a light draft, not exceeding six feet, and a low freeboard to present the smallest possible target to Confederate guns. For the design of the new class, the Navy turned once again to John Ericsson, designer of USS Monitor.

Ericsson came up with a design for a 225-foot (69 m)-long vessel with a single revolving turret containing two 11-inch (280 mm) guns, an armored upper deck, and twin screw propellers giving a top speed of around eight knots. Around the hull of the vessel, a large wooden "raft" was to be constructed, which would help increase buoyancy. Ericsson kept the design deliberately simple in keeping with the inexperience of the private shipyards which would be called upon to build them. He anticipated that each ship would take no more than forty days to complete.