Casco-class monitor

At around the same time however, the Navy created a new "monitor office" to centralize oversight of the new monitor program. The new office, located across the hall from Ericsson's design bureau, was nominally headed by Rear Admiral Francis H. Gregory, but was effectively run by Chief Engineer Alban C. Stimers, to whom was entrusted the power of setting general plans and ship specifications. Stimers, an ambitious man, was keen to take credit for the design of the new monitors and frequently visited Ericsson's bureau to make changes to the specifications.[3][5]

The greatest single alteration to the design however, came not directly from Stimers but from Admiral Joseph Smith, chief of the Bureau of Yards and Docks in Washington, D.C., who suggested that the oval hull of the ship be surrounded by large iron tanks which could be pumped full of water in order to lower the ship's freeboard still further when in combat to present an even smaller target, or drained for normal travel. Stimers liked the idea and ordered the changes, but when Ericsson saw the new plans he resigned from the project. The new plans greatly added to the design's complexity, requiring sophisticated pumping mechanisms, while the added weight would also reduce speed and buoyancy.[4]

In February 1863 the monitor office offered contracts for twenty of the new Casco-class monitors, in spite of the fact that the original architect, Ericsson, had not approved the new design. Winning bidders included prominent firms like Reaney, Son & Archbold in Chester, Pennsylvania, Wilcox & Whitney at Camden, Harlan & Hollingsworth in Wilmington, Delaware and Merrick & Sons of Philadelphia (the latter of whom subcontracted much of the work to William Cramp & Sons). A number of smaller firms were also contracted. The cost was estimated at $395,000 per ship, or approximately $8 million in total. Some shipyards, such as Cramp, were forced to substantially upgrade their ironworking facilities for the production of the new vessels.[6]

Detail drawing by Stimers for one of the Casco-class monitors

By the end of 1863, frequent design changes were causing growing problems for the contractors. Stimers and his team of thirty draftsmen at the monitor office continued to submit changes even as the vessels were in the process of production, leading to long delays. One yard in Boston received a total of 83 drawings and 120 letters of explanation from Stimers, and the specification manual for the ships grew to 92 pages of small print.[7] The final design called for a total of thirteen auxiliary engines and pumps per ship, fancy brasswork in place of cast iron, and a complex system of pipes for draining and filling the water tanks. The added weight to a ship designed with only a 15-inch (380 mm) freeboard at the outset raised questions about the ships' eventual seaworthiness.[8]

By spring of 1864, the first of the Casco-class vessels, USS Chimo, was ready for her initial trial. Putting to sea, waves washed across the deck, while the stern remained totally submerged by three or four inches (10 cm).[9] A second trial, of USS Tunxis, confirmed the disaster, with waves washing over the deck and the ship only able to make a speed of 3½ knots as opposed to the original specification of eight. Moreover, the trials were conducted "light", without the normal operational loads of coal, ammunition and stores. The ships were unseaworthy and virtually useless.[8][10][11][12]

By this stage, the twenty vessels, in various stages of completion, had cost half a million dollars apiece. Amid public scandal, the Navy set up an inquiry. Stimers was found responsible and removed from his post, and the Navy appointed experienced administrators in his place. The vessels were redesigned and refitted in order to improve buoyancy, but few of them saw active service before the end of the war and those that did were decommissioned and laid up within months, while the majority were never commissioned at all. Within a few years, all the ships of the Casco class had been retired and scrapped or otherwise disposed of.[13]