A bomb vessel, bomb ship, bomb ketch, or simply bomb was a type of wooden sailing naval ship. Its primary armament was not cannons – although bomb vessels carried a few cannons for self-defence – but mortars mounted forward near the bow and elevated to a high angle, and projecting their fire in a ballistic arc. Explosive shells or carcasses were employed rather than solid shot. Bomb vessels were specialized ships designed for bombarding fixed positions on land. In the 20th century, this naval gunfire support role was carried out by the most similar purpose-built World War I- and II-era monitors, but also by other warships now firing long-range explosive shells.

A mortar is today usually a simple, lightweight, man-portable, muzzle-loaded cannon, consisting of a smooth-bore metal tube fixed to a base plate with a lightweight bipod mount and a sight. Mortars are typically used as indirect fire weapons for close fire support with a variety of ammunition. Historically mortars were heavy siege artillery. Mortars launch explosive shells in high-arching ballistic trajectories.