The Casco-class Monitors


Following the success of USS Monitor – the ground-breaking ironclad warship, designed by Swedish-born engineer John Ericsson, that played a central role in the US Civil War Battle of Hampton Roads on 9 March 1862 – the US Navy issued a requirement for similar shallow-draft ironclads capable of operating in coastal waters and along the Mississippi River and its tributaries. Ericsson designed the new Casco-class vessels, which were deliberately kept as simple as possible to allow construction by small shipyards in as few as 40 days. Orders for a total of 20 were placed in early 1863 at the then-unprecedented total cost of $8m (roughly equivalent to $163m today).

USS Casco on the James River, 1865. Although initially a simple design, the constant alterations during construction slowed production of the vessels – and riddled them with faults. Image: Wikimedia Commons.

However, the initial plans were heavily amended by the navy’s new ‘monitor office’, run by Chief Engineer Alban Stimers. As originally designed, the class had a draft of six feet, but Stimers arbitrarily reduced this to four feet, and increased the armour protection.

A rapid succession of further ‘improvements’ eroded the original simplicity of the design. Internal ballast tanks were added so that the vessel could take on water to lower its silhouette before going into action. These required elaborate pumping equipment, which added more weight, reducing the freeboard from 15 inches (380mm) to just 3 inches (76mm). This change was the final straw for Ericsson, who promptly resigned from the project.

The sheer number of alterations drastically slowed construction. One Boston shipyard was deluged with 83 revised blueprints, while the technical manual for the class grew to 92 pages. The final design included a total of 13 pumps per ship to operate the complex system of pipes for filling and draining the ballast tanks.

Constantly awash

The first two vessels, not trialled until mid-1864, emphasised the appalling effects of the revised design. They leaked badly and their decks were almost constantly awash, while their sterns were actually submerged. What was even more alarming was that the trials were being run with both monitors at ‘light displacement’ – so without their operational loads of fuel, water, ballast, stores, and ammunition. Speed was abysmal: although their designed top speed was 8 knots, neither vessel could manage more than 3½ knots.

Strengths: None
Drawbacks: Slow, with dangerous low freeboard Constant leaks

This fiasco – coupled with costs soaring to $10m (more than $203m today) – led to Stimers’ dismissal, and Ericsson was brought back. He increased the freeboard by 22 inches (550mm), but this added an extra 130 tons to the already dangerously overweight vessels.

In desperation, the first few vessels were rearmed with a single unprotected pivot-mounted 11-inch (280mm) Dahlgren muzzle-loading smooth-bore cannon. This certainly saved weight by replacing the original heavy turret armed with two such weapons, but it left the gun crew dangerously exposed to enemy fire.

In a final bizarre twist, these rearmed vessels were also fitted with retractable spar torpedoes. This was simply an impact-fused explosive charge on a long pole, or spar, mounted in the bows. Essentially, it was an ‘explosive ram’, which was only effective against enemy shipping when used by much faster vessels than the slow Casco class.

Very few Cascos were completed before the Confederate surrender, and all 20 were hastily laid up before being scrapped in 1874/1875. •