A naval ram was a weapon carried by varied types of ships, dating back to antiquity. The weapon consisted of an underwater prolongation of the bow of the ship to form an armoured beak, usually between six and twelve feet (2-4 m) in length. This would be driven into the hull of an enemy ship in order to puncture the hull and sink, or at least disable, that ship.
The ram was a naval weapon in the Greek/Roman antiquity and was used in such naval battles as Salamis and Actium. Naval warfare rarely used sails, and the use of naval rams specifically required oarsmen over sails in order to maneuver with accuracy and speed. The Athenians were especially known for their diekplus and periplus tactics that disabled enemy ships with speed and ramming techniques.
The history of the naval rams in antiquity begins with their arrival and use at the Battle of Salamis in 480 BCE. The evidence available to suggest an earlier date for the first appearance of the naval ram relies on stylized images found on Greek pottery and jewelry, as well as somewhat ambiguous Assyrian reliefs and paintings. Stronger evidence exists that the naval ram most likely evolved from cutwaters, structures designed to support the keel-stem joint and allow for greater speed and dynamism in the water. Naval rams required incredible force and manpower, two requirements that most likely hindered the use of the ram until the rise of the Athenian fleet. However, ancient shipbuilding eventually grew to include pegged mortise and tenon construction, heavier designs, and a wineglass shaped hull, which allowed for the strength and sturdiness necessary for a ram to be effective in battle without the danger of twisting off. There is also evidence to suggest that cutwaters were sheathed in thin metal as well, which correlates to the metal casings on rams, specifically bronze. All of the factors point to a Greek invention of the naval ram, and credit must also be given for their pioneering use of it against the Persians in the Battle of Salamis.
The Athlit ram found off of the coast of Israel is the best example of naval rams discovered to this day. It is thought to be one of the main weapons of the Athenian trireme, and its construction implies advanced technology developed over long periods of time. The ram is special because heavy timbers were shaped and attached to the hull, and then a bronze case was created to fit around the timbers for added strength. The evidence for this lies with the bits of timber found still inside when the Athlit ram was discovered The blunt edge of the ram and the patterned protrusion would have been enough to disable a rigid ship and disperse the force of the impact on the attacking ship to prevent the twisting off of the ram or damage to the ship itself. Rams were always made of bronze, and weighed anywhere from 8 to 20 tons. The Athlit Ram is 226 cm long with a maximum width of 76 cm, a maximum height of 96 cm. The bronze that makes up the shell contains 9.78% tin with traces of lead and other elements. The shell was cast as a single piece to fit the timbers it protects perfectly. This must have been a difficult endeavor without the technical equipment we have now. The ram can be separated into three parts, the driving center, the bottom plate, and the cowl. The driving center is 30 cm long and 76 cm wide. This is the area of the ram that makes contact with enemy vessels in battle. The front wall of the head of the ram has the thickest layer of casting at 6.8 cm for extra protection during battle. The surface of the ram was decorated with several symbols. On each side, an eagle head, a helmet, and an eight point star. These symbols are similar in dimension, but contain many inconsistencies with each other, suggesting that they were made from the same mold. The ram has a handle depicting a tri-form thunderbolt. It is attached with mortis and tenon joints pegged with 15 mm oak pegs. The wales and the ramming timber are made to interlock for extra strength. The bottom of the ram features a mortis cut into the ramming timber to fit the most forward end of the keel which has been formed into a four centimeter thick and ten centimeter long tenon. The ramming face is flat, so the ram can disengage contact easily and without being pulled or twisted off.
In more modern examples, many 19th Century ironclad battleships were equipped with rams. The speed, power, and maneuverability allowed by steam propulsion again raised the idea of using the ship's hull as a weapon. As early as 1840, the French admiral Nicolas-Hippolyte Labrousse proposed building a ram steamship, and by 1860, Dupuy de Lôme had designed an ironclad with a ram. The quick success of the CSS Virginia's ramming attack on the USS Cumberland at the Battle of Hampton Roads in 1862 attracted much attention and caused many navies to re-think the ram. The first coastal battleship, France's Taureau, was built in 1863 for the purpose of attacking warships at anchor or in narrow straits, and was armed with a ram.  Many ironclad ships were designed specifically to ram opponents, such as the General Price, pictured to the right. In ships of this type, the armour belt was prolonged to brace both sides of the ram to increase structural integrity.
The theory behind the revival of the weapon derived from the fact that, in the period around 1860, armour held superiority over the ship-mounted cannon. It was believed that an armoured warship could not be seriously damaged by the naval artillery in existence at the time. In order to achieve a decisive result in a naval engagement, therefore, alternative methods of action were believed to be necessary. As it followed, from the same belief, that a ship armed with a ram could not be seriously damaged by the gunfire of its intended victim, the ram became, for a brief period, the main armament of many battleships. It was observed that the guns placed on the Taureau were there "with the sole function of preparing the way for the ram."
The frequent use of ramming as a tactic in the Battle of Lissa (1866) and, to a lesser extent, at the Battle of Iquique also led to many late nineteenth century naval designers equipping their warships with ram bows. This only really aggravated a number of incidents of ships being sunk by their squadron-mates in accidental collisions as ramming never featured as a viable battle tactic again. The fixation on ramming may also have inhibited the development of gunnery.
When it became clear, towards the end of the nineteenth century, that breech-loading cannon could hit, and hit effectively, enemy ships at several thousand yards range, the ineffectiveness of the ram became clear and ships ceased to be fitted with them.
No other ironclad was ever sunk by an enemy ship in time of war by the use of the ram, although the ram was regarded by all major navies for some thirty years as primary battleship armament. A number of ships were, however, rammed in peacetime by ships of their own navy. The most serious in terms of loss of life was the collision between HMS Victoria and HMS Camperdown, which took place in the Mediterranean in 1893. The only battleship over submarine victory in history occurred during World War I, when the battleship HMS Dreadnought rammed and sank a German U-Boat, but Dreadnought's bow was not intended for ramming enemy vessels.
The torpedo ram was a hybrid torpedo boat combining a ram with torpedo tubes. Incorporating design elements from the cruiser and the monitor, it was intended to provide a small and inexpensive weapon systems for coastal defence and other littoral combat.
Like monitors, torpedo rams operated with very little freeboard, sometimes with only inches of hull rising above the water, exposing only their funnels and turrets to enemy fire. In addition to the guns in their turrets, they were also equipped with torpedoes. Early designs incorporated a spar torpedo that could be extended from the bow and detonated by ramming a target. Later designs used tube-launched self-propelled torpedoes, but retained the concept of ramming, resulting in designs like HMS Polyphemus, which had five torpedo tubes, two each port and starboard and one mounted in the centre of her reinforced ram bow.