42-pounder weapons were of particular concern to military commanders because they were structurally weaker and more prone to exploding than purpose-built rifled cannons. Additionally, the close confines of riverine combat greatly increased the threat of boarding parties. The 12-pounder howitzer was equipped to address that concern and was not used in regular combat. See also Union Navy Anaconda Plan Mississippi Squadron References External links Pictures of USS Baron de Kalb Building the City Class Ironclads Documentary Ships of the Union Navy Steamships of the United States Navy Gunboats of the United States Navy American Civil War patrol vessels of the United States Ships built in St. Louis Shipwrecks of the Yazoo River Shipwrecks of the American Civil War Ships sunk by mines 1861 ships Maritime incidents in July 1863