HMS Aubrietia (K96)

Naval trawlers are vessels built along the lines of a fishing trawler but fitted out for naval purposes; they were widely used during the First and Second World Wars. Some—known in the Royal Navy as "Admiralty trawlers"— were purpose-built to naval specifications, others adapted from civilian use. Fishing trawlers were particularly suited for many naval requirements because they were robust vessels designed to work heavy trawls in all types of weather, and had large clear working decks. A minesweeper could be created by replacing the trawl with a mine sweep. Adding depth charge racks on the deck, ASDIC sonar below, and a 3-inch (76 mm) or 4-inch (102 mm) gun in the bow equipped the trawler for anti-submarine duties.

The Hunt class was a class of escort destroyer of the Royal Navy. The first vessels were ordered early in 1939, and the class saw extensive service in the Second World War, particularly on the British east coast and Mediterranean convoys. They were named after British fox hunts. The modern Hunt-class GRP hulled mine countermeasure vessels maintain the Hunt names lineage in the Royal Navy.

The Kingfisher class was a class of nine patrol sloops of the British Royal Navy built in three groups of three each during the 1930s, that saw service during World War II, mainly on East Coast convoys in the North Sea.

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.

Length between perpendiculars is the length of a ship along the summer load line from the forward surface of the stem, or main bow perpendicular member, to the after surface of the sternpost, or main stern perpendicular member. When there is no sternpost, the centerline axis of the rudder stock is used as the aft end of the length between perpendiculars.

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 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.

The BL 4-inch Mk IX naval gun was a British medium-velocity naval gun introduced in 1917 as secondary armament on the Renown-class battlecruisers and Glorious-class "large light cruisers", but which served most notably as the main armament on Flower-class corvettes throughout World War II.

The Lewis gun is a First World War–era light machine gun. Designed privately in the United States though not adopted there, the design was finalised and mass-produced in the United Kingdom, and widely used by troops of the British Empire during the war. It had a distinctive barrel cooling shroud and top-mounted pan magazine. The Lewis served to the end of the Korean War, and was widely used as an aircraft machine gun during both World Wars, almost always with the cooling shroud removed, as air flow during flight offered sufficient cooling.

Laying the keel or laying down is the formal recognition of the start of a ship's construction. It is often marked with a ceremony attended by dignitaries from the shipbuilding company and the ultimate owners of the ship.

Greenock is a town and administrative centre in the Inverclyde council area in Scotland, United Kingdom and a former burgh within the historic county of Renfrewshire, located in the west central Lowlands of Scotland. It forms part of a contiguous urban area with Gourock to the west and Port Glasgow to the east.

Ceremonial ship launching involves the performance of ceremonies associated with the process of transferring a vessel to the water. It is a nautical tradition in many cultures, dating back thousands of years, to accompany the physical process with ceremonies which have been observed as public celebration and a solemn blessing, usually but not always, in association with the launch itself.

Horsforth is a town and civil parish in the City of Leeds, West Yorkshire, England, five miles north-west of Leeds city centre. Historically a village within the West Riding of Yorkshire, it had a population of 18,895 at the 2011 Census. It became part of the City of Leeds metropolitan borough in 1974. In 1999, a civil parish was created for the area, and the parish council voted to rename itself a town council. The area is within the Horsforth ward of Leeds City Council, which also includes the southern part of Rawdon.

The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. The campaign peaked from mid-1940 through to the end of 1943.

OB 318 was a North Atlantic convoy which ran during the Battle of the Atlantic in World War II. During Operation Primrose Royal Navy convoy escorts HMS Bulldog, Broadway and Aubrietia captured U-110 with an intact Enigma machine and a wealth of signals intelligence, which led to the Allied breakthrough into cracking the German naval Enigma code.

German submarine U-110 was a Type IXB U-boat of Nazi Germany's Kriegsmarine that operated during World War II. She was captured by the Royal Navy on 9 May 1941 and provided a number of secret cipher documents to the British. U-110's capture, later given the code name "Operation Primrose", was one of the biggest secrets of the war, remaining so for seven months. President Franklin D. Roosevelt was only told of the capture by Winston Churchill in January 1942.

The Enigma machine is a cipher device developed and used in the early- to mid-20th century to protect commercial, diplomatic, and military communication. It was employed extensively by Nazi Germany during World War II, in all branches of the German military. The Enigma machine was considered so secure that it was used to encipher the most top-secret messages.

HMS Bulldog (H91) was a B-class destroyer built for the Royal Navy (RN) between 1929 to 1931. Initially assigned to the Mediterranean Fleet, she transferred to the Home Fleet in 1936. During the Spanish Civil War of 1936–1939, the ship spent considerable time in Spanish waters, enforcing the arms blockade imposed by Britain and France on both sides of the conflict. Bulldog saw service throughout World War II on convoy escort duty during the Battle of the Atlantic and in the Arctic. Her most notable actions were the capture of an Enigma machine and codebooks from the German submarine U-110 in 1941, sinking another German submarine in 1944 and taking the surrender of the German garrisons on the Channel Islands on 9 May 1945. Surplus after the war, she was broken up for scrap in 1946.

Freetown is the capital and largest city of Sierra Leone. It is a major port city on the Atlantic Ocean and is located in the Western Area of the country. Freetown is Sierra Leone's major urban, economic, financial, cultural, educational and political centre, as it is the seat of the Government of Sierra Leone. The population of Freetown was 1,055,964 at the 2015 census.

Operation Torch was an Allied invasion of French North Africa during the Second World War. Torch was a compromise operation that met the British objective of securing victory in North Africa while allowing American armed forces the opportunity to engage in the fight against Nazi Germany on a limited scale. It was the first mass involvement of US troops in the European–North African Theatre, and saw the first major airborne assault carried out by the United States.

The Hedgehog was a forward-throwing anti-submarine weapon that was used primarily during the Second World War. The device, which was developed by the Royal Navy, fired up to 24 spigot mortars ahead of a ship when attacking a U-boat. It was deployed on convoy escort warships such as destroyers and corvettes to supplement the depth charges.

The Strait of Gibraltar, also known as the Straits of Gibraltar, is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates the Iberian Peninsula in Europe from Morocco in Africa.

Operation Dragoon was the code name for the landing operation of the Allied invasion of Provence on 15 August 1944. Although initially designed to be executed in conjunction with Operation Overlord, the Allied landing in Normandy, a lack of available resources led to a cancellation of the second landing. By July 1944 the landing was reconsidered, as the clogged-up ports in Normandy did not have the capacity to adequately supply the Allied forces. Concurrently, the High Command of the French Liberation Army pushed for a revival of the operation that would include large numbers of French troops. As a result, the operation was finally approved in July to be executed in August.