The Collaborative International Dictionary
Columbiad \Co*lum"bi*ad\, n. [From Columbia the United States.] (Mil.) A form of seacoast cannon; a long, chambered gun designed for throwing shot or shells with heavy charges of powder, at high angles of elevation.
Note: Since the War of 1812 the Columbiad has been much modified, especially by General Rodman, and the improved form now used in seacoast defense is often called the Rodman gun.
Rodman gun refers to a series of American Civil War–era columbiads designed by Union artilleryman Thomas Jackson Rodman (1815–1871). The guns were designed to fire both shot and shell. These heavy guns were intended to be mounted in seacoast fortifications. They were built in 8-inch, 10-inch, 13-inch, 15-inch, and 20-inch bore. Other than size, the guns were all nearly identical in design, with a curving bottle shape, large flat cascabels with ratchets or sockets for the elevating mechanism. Rodman guns were true guns that did not have a howitzer-like powder chamber, as did many earlier columbiads. Rodman guns differed from all previous artillery because they were hollow cast, a new technology that Rodman developed that resulted in cast iron guns that were much stronger than their predecessors.