Unfinished by the end of the war, their construction was suspended in November 1865 and the unseasoned wood of their hulls rotted while they were still on the building stocks.

John Lenthall, Chief of the Bureau of Construction and Repair, ordered Benjamin F. Delano, naval constructor at New York City, to design a wooden-hulled ironclad that would carry her armament in two gun turrets.

[1] Gideon Welles, Secretary of the Navy, called them enlarged versions of the Miantonomoh-class monitors with greater speed and "adapted to coast service", meaning more seaworthy.

The Kalamazoo's wrought iron side armor consisted of two layers of three-inch plates, backed by 21 inches of wood, six feet in height.

[4] The ships' main armament consisted of four smoothbore, muzzle-loading, 15-inch (381 mm) Dahlgren guns mounted in two twin-gun turrets.

Vice Admiral David D. Porter ordered that Colossus be rebuilt to carry 10 large broadside guns and fitted with iron masts in a ship rig, but this never happened.