The boat howitzer derived from a requirement realized during the Mexican–American War. During that war, naval landing parties were armed with a variety of army ordnance, often too heavy and cumbersome for use with the landing boats. Dahlgren first experimented with standard army-issue 12-pounder mountain howitzers before devising his own system of guns. The boat howitzers came in four basic types: small, light (or medium), and heavy versions of the 12-pounder and a larger 24-pounder. All conformed to the same basic shape, straight gun tubes with no adorning bands or clefts. Elevation was made via a screw threaded into the knob at the breech. Instead of by traditional trunnions, the guns were attached to the carriage by a loop under the barrel. The Dahlgren system also included mounting carriages that facilitated various employments of the guns. A single-axle metal carriage was designed for shore use. A bed-type carriage was used on small boats, with a rail system to allow the gun to be trained fore, aft and broadside of the boat. A similar mount was offered for shipboard use. The system of boat howitzers was used by the Navy well into the 1890s, with some examples used in ceremonial purposes into the 20th Century.