Displacement (ship)

The draft or draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel). The draught of the vessel is the maximum depth of any part of the vessel, including appendages such as rudders, propellers and drop keels if deployed. Draft determines the minimum depth of water a ship or boat can safely navigate. The related term air draft is the maximum height of any part of the vessel above the water.

Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front).

The slide rule is a mechanical analog computer which is used primarily for multiplication and division and for functions such as exponents, roots, logarithms, and trigonometry. It is not typically designed for addition or subtraction, which is usually performed using other methods, like using an abacus. Maximum accuracy for standard linear slide rules is about three decimal significant digits, while scientific notation is used to keep track of the order of magnitude of results.

The tonne is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton, and the long ton. It is equivalent to approximately 2204.6 pounds, 1.102 short tons, and 0.984 long tons. The official SI unit is the megagram, a less common way to express the same mass.

The first ship named in honor of Rear Admiral Aaron Ward, USS Aaron Ward (DD-132) was a Wickes-class destroyer in service with the United States Navy. In 1940, she was transferred to the Royal Navy and renamed HMS Castleton.

USS Abel P. Upshur (DD-193) was a Clemson-class destroyer in the service of the United States Navy and United States Coast Guard until transferred to the United Kingdom in 1940. During World War II, she served in the Royal Navy as HMS Clare.

The waterline is the line where the hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line, that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of waves that may arise. Varying water temperatures will affect a ship's draft, because warm water is less dense than cold water, providing less buoyancy. In the same way, fresh water is less dense than salinated or seawater with a similar lessening effect upon buoyancy.

The Washington Naval Treaty, also known as the Five-Power Treaty, was a treaty signed during 1922 among the major Allies of World War I, which agreed to prevent an arms race by limiting naval construction. It was negotiated at the Washington Naval Conference in Washington, D.C. from November 1921 to February 1922 and signed by the governments of the United Kingdom, United States, France, Italy, and Japan. It limited the construction of battleships, battlecruisers and aircraft carriers by the signatories. The numbers of other categories of warships, including cruisers, destroyers, and submarines, were not limited by the treaty, but those ships were limited to 10,000 tons displacement each.