铁甲舰又译装甲舰，是19世纪下半叶早期的一种蒸汽式军舰，外覆有坚硬的铁或钢制装甲。由于木造军舰无力抵御炮弹的轰炸，铁甲舰便应运而生。1859年11月，由法国海军领衔的全球第一艘主力铁甲战舰光荣号（La Gloire）首度启航。英国皇家海军自1856年起筹划发展装甲战舰，1857年顺利拟定装甲护卫舰草稿图，但1859年初皇家海军选择打造二艘铁甲巡防舰，并于1861年决议朝全装甲舰队发展。在美国内战期间铁甲舰首度交锋后，帆船时代无装甲（木质船壳）的战列舰已明显居于弱势，铁甲舰便取代之，跃身成为水战最强大的船舰。此类型的船舰后来甚至主宰了美国内战。

An ironclad is a steam-propelled warship protected by iron or steel armor plates used in the early part of the second half of the 19th century. The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells. The first ironclad battleship, Gloire, was launched by the French Navy in November 1859. The British Admiralty had been considering armored warships since 1856 and prepared a draft design for an armored corvette in 1857; in early 1859 the Royal Navy started building two iron-hulled armored frigates, and by 1861 had made the decision to move to an all-armored battle fleet. After the first clashes of ironclads (both with wooden ships and with one another) took place in 1862 during the American Civil War, it became clear that the ironclad had replaced the unarmored ship of the line as the most powerful warship afloat. This type of ship would come to be very successful in the American Civil War.