HMS Clacton (J151)

The displacement or displacement tonnage of a ship is its weight. As the term indicates, it is measured indirectly, using Archimedes' principle, by first calculating the volume of water displaced by the ship, then converting that value into weight. Traditionally, various measurement rules have been in use, giving various measures in long tons. Today, tonnes are more commonly used.

Length overall is the maximum length of a vessel's hull measured parallel to the waterline. This length is important while docking the ship. It is the most commonly used way of expressing the size of a ship, and is also used for calculating the cost of a marina berth.

The beam of a ship is its width at its widest point. The maximum beam (BMAX) is the distance between planes passing through the outer extremities of the ship, beam of the hull (BH) only includes permanently fixed parts of the hull, and beam at waterline (BWL) is the maximum width where the hull intersects the surface of the water.

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.

In a navy, a rate, rating or bluejacket is a junior enlisted sailor who is not a warrant officer or commissioned officer. Depending on the country and navy that uses it, the exact term and the range of ranks that it refers to may vary.

The knot is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h. The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE), while kt is also common, especially in aviation, where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. The knot is used in meteorology, and in maritime and air navigation. A vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.

Fuel oil is any of various fractions obtained from the distillation of petroleum. Such oils include distillates and residues. Fuel oils include heavy fuel oil, marine fuel oil (MFO), bunker fuel, furnace oil (FO), gas oil (gasoil), heating oils, diesel fuel and others.

The 2-pounder gun, officially the QF 2-pounder and universally known as the pom-pom, was a 40 mm (1.6 in) British autocannon, used as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing. This QF 2-pounder was not the same gun as the Ordnance QF 2-pounder, used by the British Army as an anti-tank gun and a tank gun, although they both fired 2 lb (0.91 kg), 40 mm (1.6 in) projectiles.

The Oerlikon 20 mm cannon is a series of autocannons, based on an original German Becker Type M2 20 mm cannon design that appeared very early in World War I. It was widely produced by Oerlikon Contraves and others, with various models employed by both Allied and Axis forces during World War II. Many versions of the cannon are still used today.

A depth charge is an anti-submarine warfare (ASW) weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive hydraulic shock. Most depth charges use high explosive charges and a fuze set to detonate the charge, typically at a specific depth. Depth charges can be dropped by ships, patrol aircraft, and helicopters.

Ailsa Shipbuilding Company was a Scottish shipbuilding company based in Troon and Ayr, Ayrshire.

Troon is a town in South Ayrshire, situated on the west coast of Ayrshire in Scotland, about eight miles north of Ayr and three miles northwest of Glasgow Prestwick Airport.

Essex is a county in the East of England. One of the home counties, it borders Suffolk and Cambridgeshire to the north, the North Sea to the east, Hertfordshire to the west, Kent across the estuary of the River Thames to the south, and Greater London to the south and south-west. There are three cities in Essex: Southend, Colchester and Chelmsford, in order of population. For the purposes of government statistics, Essex is placed in the East of England region. There are four definitions of the extent of Essex, the widest being the ancient county. Next, the largest is the former postal county, followed by the ceremonial county, with the smallest being the administrative county—the area administered by the County Council, which excludes the two unitary authorities of Thurrock and Southend-on-Sea. The ceremonial county occupies the eastern part of what was, during the Early Middle Ages, the Anglo-Saxon Kingdom of Essex. As well as rural areas and urban areas, it forms part of the wider Home Counties of England.

Clacton-on-Sea is a seaside town in the Tendring District in the county of Essex, England. It is located on the Tendring Peninsula and is the largest settlement in the Tendring District with a population of 56,874 (2016). The town is situated around 76.9 miles north-east of Central London, 40 miles from Chelmsford, 57.9 miles from Southend-on-Sea, 15.8 miles south-east of Colchester Town and 16.3 miles south of Harwich. The town is a seaside resort, located on the east coast of England.

Corsica is an island in the Mediterranean Sea and one of the 18 regions of France. It is the fourth-largest island in the Mediterranean and lies southeast of the French mainland, west of the Italian Peninsula and immediately north of the Italian island of Sardinia, which is the land mass nearest to it. A single chain of mountains makes up two-thirds of the island. As of January 2023, it had a population of 351,255.

La Maddalena is a town and comune located on the islands of the Maddalena archipelago in the province of Sassari, northern Sardinia, Italy.

Bastia is a commune in the department of Haute-Corse, Corsica, France. It is located in the northeast of the island of Corsica at the base of Cap Corse. It also has the second-highest population of any commune on the island after Ajaccio and is the capital of the Bagnaja region and of the department.

A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, any vessel or a particular vessel type, akin to anti-infantry vs. anti-vehicle mines. Naval mines can be used offensively, to hamper enemy shipping movements or lock vessels into a harbour; or defensively, to protect friendly vessels and create "safe" zones. Mines allow the minelaying force commander to concentrate warships or defensive assets in mine-free areas giving the adversary three choices: undertake an expensive and time-consuming minesweeping effort, accept the casualties of challenging the minefield, or use the unmined waters where the greatest concentration of enemy firepower will be encountered.