The Harbour Defence Motor Launch (HDML) was a British small motor vessel of the Second World War.

The HDML was designed by W J Holt at the Admiralty

Admiralty

The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...

 in early 1939. During the war, 486 HDMLs were constructed, mainly by yacht builders, in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 and a number of other allied countries. In view of their later expanded combat roles in some Commonwealth

Commonwealth of Nations

The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

 navies some HDMLs were re-designated as Seaward Defence Motor Launches (SDML) or Seaward Defence Boats (SDB).

Design and construction

HDMLs had a round bilge heavy displacement hull

Hull (watercraft)

A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

 72 feet (21.9 m) long with a beam of 16 feet (4.9 m) and a loaded draught of 5 feet (1.5 m). Loaded displacement was 54 tons. The hull had a pronounced flare forward to throw the bow wave

Bow wave

A bow wave is the wave that forms at the bow of a ship when it moves through the water. As the bow wave spreads out, it defines the outer limits of a ship's wake. A large bow wave slows the ship down, poses a risk to smaller boats, and in a harbor can cause damage to shore facilities and moored ships...

 clear and provided considerable lift to prevent all but the heaviest seas from coming aboard. Although seaworthy, the boat had a considerable tendency to roll, especially when taking seas at anything other than directly ahead or astern. The cause was the round bilge midship section and a considerable reserve of stability, the effect of which was to impart a powerful righting moment if the boat was pushed over in a seaway. This, coupled with the round bilged hull and lack of bilge keels, would set up a rapid and violent rolling.

One of the design criteria was that the boat had to be capable of turning inside the turning circle of a submerged submarine. To achieve this, HDMLs were fitted with two very large rudder

Rudder

A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...

s and, to reduce resistance to turning, the keel

Keel

In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

 ended 13 ft (4 m) before the stern. A side effect of this was that the boat lacked directional stability

Directional stability

Directional stability is stability of a moving body or vehicle about an axis which is perpendicular to its direction of motion. Stability of a vehicle concerns itself with the tendency of a vehicle to return to its original direction in relation to the oncoming medium when disturbed away from...

 and was extremely difficult to hold on a straight course.

The hull was of round bilge wooden construction, planked with two diagonally opposed skins with a layer of oiled calico between them – known as a “double-diagonal” technique. The hull was completed with frames or “timbers” riveted perpendicularly from the keel to the gunwale

Gunwale

The gunwale is a nautical term describing the top edge of the side of a boat.Wale is the same word as the skin injury, a wheal, which, too, forms a ridge. Originally the gunwale was the "Gun ridge" on a sailing warship. This represented the strengthening wale or structural band added to the design...

 on the inside of the planking, forming a very strong hull. The hull was further strengthened by the addition of longitudinal stringer

Stringer

Stringer may refer to:* Stringer , a type of freelance journalism* Stringer * Stringer , or longeron, a strip of wood or metal to which the skin of an aircraft is fastened...

s riveted inside the timbers together with further timbers, known as "web frames". They are fastened inside the stringers opposite every third main timber. HDMLs were fitted with a deeper section rubbing strake

Strake

A strake is part of the shell of the hull of a boat or ship which, in conjunction with the other strakes, keeps the sea out and the vessel afloat...

 aft. Its purpose was to roll depth charges (kept in and delivered from racks on the side decks), clear of the hull and propellers.

Most HDML hulls were planked in mahogany

Mahogany

The name mahogany is used when referring to numerous varieties of dark-colored hardwood. It is a native American word originally used for the wood of the species Swietenia mahagoni, known as West Indian or Cuban mahogany....

, but as the war progressed this became scarce, larch

Larch

Larches are conifers in the genus Larix, in the family Pinaceae. Growing from 15 to 50m tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south...

 was used although this tended to lead to leaky hulls. The decks were also of double-diagonal construction and generally made of softwood

Softwood

The term softwood is used to describe wood from trees that are known as gymnosperms.Conifers are an example. It may also be used to describe trees, which tend to be evergreen, notable exceptions being bald cypress and the larches....

. Boats operating in tropical waters (including the Mediterranean) were sheathed in copper below the waterline to prevent the attack of marine borers.

In order to lessen the chances of the boat sinking in the event of damage to the hull, they were divided into six watertight compartments. Provided that the bulkheads

Bulkhead (partition)

A bulkhead is an upright wall within the hull of a ship or within the fuselage of an airplane. Other kinds of partition elements within a ship are decks and deckheads.-Etymology:...

 were not damaged, the boat could remain afloat with any one compartment flooded.

Accommodation

HDMLs were designed to accommodate a crew of ten. There were berths for six rating

Naval rating

A Naval Rating is an enlisted member of a country's Navy, subordinate to Warrant Officers and Officers hence not conferred by commission or warrant...

s in the fore cabin, which also contained a galley with a coal fired

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 stoveAdmiralty Pattern 3160 In the forepeak, there was a Baby Blake sea toilet and hand wash basin

Sink

A sink is a bowl-shaped plumbing fixture used for washing hands, for dishwashing or other purposes. Sinks generally have taps that supply hot and cold water and may include a spray feature to be used for faster rinsing...

. The officers were berthed in the after end of the boat; the petty officers

Petty Officer

A petty officer is a non-commissioned officer in many navies and is given the NATO rank denotion OR-6. They are equal in rank to sergeant, British Army and Royal Air Force. A Petty Officer is superior in rank to Leading Rate and subordinate to Chief Petty Officer, in the case of the British Armed...

 being in a cabin on the port side just aft of the engine room, they had their own separate toilet and hand wash basin. A small “Courtier” coal fired stove provided heating.

The commissioned officers

Officer (armed forces)

An officer is a member of an armed force or uniformed service who holds a position of authority. Commissioned officers derive authority directly from a sovereign power and, as such, hold a commission charging them with the duties and responsibilities of a specific office or position...

 had comparatively roomy accommodation in the wardroom

Wardroom

The wardroom is the mess-cabin of naval commissioned officers above the rank of Midshipman. The term the wardroom is also used to refer to those individuals with the right to occupy that wardroom, meaning "the officers of the wardroom"....

 aft, although it suffered from being situated above the propeller shafts and therefore subject to noise and vibration. The wardroom also contained the ship’s safe, a dining table and seating, a wine and spirit locker, a small coal stove and a tiny footbath.

The boat’s radio room was a small compartment situated aft on the starboard side, adjacent to the petty officers’ toilet.

The chartroom was located on the main deck. It contained the chart table, a casual berth and a second steering position. On the forward bulkhead a navigational switchboard was fitted, which included a duplicate set of engine revolution indicators, switches for the navigation lights, “Kent” clear-view screens and the “action-stations” alarm.

The main steering position was on the open bridge where the two engine room telegraphs were fitted. There were also voice pipes connected to the inside steering position, the engine room, the radio room and the wardroom.

Engine room

The HDMLs had a manned engine room which usually comprised two engine room staff when in Royal Naval service. There was no direct bridge control of the main engines or machinery. A small ship's telegraph

Engine order telegraph

An engine order telegraph or E.O.T., often also chadburn, is a communications device used on a ship for the pilot on the bridge to order engineers in the engine room to power the vessel at a certain desired speed...

 system was used in conjunction with a buzzer system, with predetermined signals for the communication of orders between the engineer and master.

The engineer operated the machinery from a position between the main engine propulsion gearboxes on the centreline of the vessel. This was generally done in the sitting down position, using a removable seat which was hung from the engine room access ladder. Four levers were used to control the two engine's rpm settings and the direction of drive to the propellers via reversing gearboxes. A governor (speed control) control lever was used to adjust the engine revolutions, and a gearbox lever was used with positions for ahead, neutral and reverse.

Settings for the engine governor controls (HDMLs fitted with Gardner 8L3s) were "Slow" 250 rpm, "Half" 600 rpm, "Full" 800 rpm and "Emergency Full" 900 rpm, and those settings were possible with the gearboxes in ahead or astern. The vessel's telegraphs indicated the required settings for all levers at any one time.
Other operations included the monitoring of the water jacket temperatures of both prime movers. Gardner design engineers designed the early marine variants of the 8L3s to be direct salt-water–cooled, with an allowance for corrosion included in the water jacket wall thickness. To maintain the correct operating temperature of 62 degrees C, a bypass valve was incorporated in the cooling circuit. This allowed varying amounts of the coolant to be diverted back to the feed side of the pump, thus raising the water temperature before circulating it around the engine. This in turn resulted in a higher overall engine temperature.
A third engine was installed within the machinery space to provide motive power for electrical generation and to operate the fire and bilge pump set. This was also a Gardner sourced engine of the type 1L2, and was a single cylinder hand start unit producing 7.5 hp.

Other features of the machinery space were five liquid storage tanks. Two large fuel oil tanks on the centre of each wing, with two day service fuel oil tanks just forward of the former, which supplied fuel to all engines by gravity feed. The fifth tank was used to store lubrication oil, and this was generally sited on the Port side aft area of the space. The adjacent space on the STB side provided space for the engineer's work bench.

Armament

Initially HDMLs were commonly fitted with a QF 2-pounder gun

QF 2 pounder naval gun

The 2-pounder gun, officially designated the QF 2-pounder and universally known as the pom-pom, was a 1.575 inch British autocannon, used famously as an anti-aircraft gun by the Royal Navy. The name came from the sound that the original models make when firing...

 on the foredeck, an Oerlikon 20 mm

Oerlikon 20 mm cannon

The Oerlikon 20 mm cannon is a series of autocannons, based on an original design by Reinhold Becker of Germany, very early in World War I, and widely produced by Oerlikon Contraves and others...

 High Angle/Low Angle cannon on the stern cabin which could be used against surface targets or anti-aircraft defence and a 0.303 Vickers machine gun

Vickers machine gun

Not to be confused with the Vickers light machine gunThe Vickers machine gun or Vickers gun is a name primarily used to refer to the water-cooled .303 inch machine gun produced by Vickers Limited, originally for the British Army...

 on each side of the bridge

Bridge (ship)

The bridge of a ship is the room or platform from which the ship can be commanded. When a ship is underway the bridge is manned by an OOW aided usually by an AB acting as lookout...

. They carried 6 to 8 depth charges on the aft decks. The 2-pounder guns were not particularly accurate, possibly because of the boats' tendency to roll, and many were replaced by another 20 mm Oerlikon HA/LA gun.

Service

HDMLs were originally intended for the defence of estuarial and local waters

Brown-water navy

Brown-water navy is a term that originated in the United States Navy, referring to the small gunboats and patrol boats used in rivers, along with some of the larger ships that supported them as "mother ships," from which they operated...

, they proved such a seaworthy and versatile design that they were used in every theatre of operations as the war progressed. They were to be found escorting convoys off the West Coast of Africa

British West Africa

British West Africa was the collective name for British colonies in West Africa during the colonial period, either in the general geographical sense or more specifically those comprised in a formal colonial administrative entity...

, carrying out covert activities in the Mediterranean and undertaking anti-submarine

Anti-submarine warfare

Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

 patrols off Iceland.

HDMLs were initially transported as deck cargo on larger ships for foreign service, which is why their length was restricted to 72 feet. Later in the war, with many merchant ships

Merchant vessel

A merchant vessel is a ship that transports cargo or passengers. The closely related term commercial vessel is defined by the United States Coast Guard as any vessel engaged in commercial trade or that carries passengers for hire...

 being sunk, it was found to be much safer to move them abroad under their own power. Some HDMLs (including 1301), undertook fairly substantial ocean voyages. Many belonging to the Mediterranean fleet sailed from the UK to Malta via Gibraltar

Gibraltar

Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

 in convoy, voyages which necessitated going well out into the Atlantic in order to keep clear of the enemy occupied coast. Three HDMLs were fitted with a second mast and sails with the intention of sailing to the Caribbean

British West Indies

The British West Indies was a term used to describe the islands in and around the Caribbean that were part of the British Empire The term was sometimes used to include British Honduras and British Guiana, even though these territories are not geographically part of the Caribbean...

. In the event, they did not make this voyage, joining the Mediterranean fleet instead.

HDMLs were normally manned by Royal Naval Volunteer Reserve

Royal Naval Reserve

The Royal Naval Reserve is the volunteer reserve force of the Royal Navy in the United Kingdom. The present Royal Naval Reserve was formed in 1958 by merging the original Royal Naval Reserve and the Royal Naval Volunteer Reserve , a reserve of civilian volunteers founded in 1903...

 (RNVR) officers with temporary commissions, and “hostilities only” ratings. The crews, however, gained an enviable reputation for their skill and expertise in the handling and fighting of their vessels.

Post-war

After the war HDMLs were adapted for other purposes, such as surveying, or were allocated to RNVR units to provide valuable seagoing experience for this important part-time navy. Some were sold to countries such as Burma, Malaya, Sri Lanka and the Philippines and became the backbone of those countries naval forces. Many were sold out of naval service to become private motor yacht

Yacht

A yacht is a recreational boat or ship. The term originated from the Dutch Jacht meaning "hunt". It was originally defined as a light fast sailing vessel used by the Dutch navy to pursue pirates and other transgressors around and into the shallow waters of the Low Countries...

s or passenger boats, purposes for which they were ideally suited, with their diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

s and roomy accommodation. Such was the superior design and build of these craft, that a number still survive today in their civilian role. Others continued in government service as Cutters for HM Customs

Her Majesty's Customs and Excise

HM Customs and Excise was, until April 2005, a department of the British Government in the UK. It was responsible for the collection of Value added tax , Customs Duties, Excise Duties, and other indirect taxes such as Air Passenger Duty, Climate Change Levy, Insurance Premium Tax, Landfill Tax and...

, before finding their way onto the civilian market at the end of their working lives.

The last known active HDML is ML1387 (Medusa, one of a handful which were the last in Royal Naval service. ML1387 has recently undergone an extensive refit to keep her seagoing.

HDML survivors

The Medusa Trust maintains an extensive archive of documents, photographs and records of nearly all 480 HDMLs and their crews.
The HDML 1301 is privately owned.

Builders

This is a partial list of known builders

Australia

• A.McFarlane and Sons, Birkenhead
  Birkenhead
  Birkenhead is a town within the Metropolitan Borough of Wirral in Merseyside, England. It is on the Wirral Peninsula, along the west bank of the River Mersey, opposite the city of Liverpool...
  
  , South Australia
  South Australia
  South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
  
  
• E.A.Jack, Trevallyn
  Trevallyn, Tasmania
  Trevallyn is a suburb of Launceston, in the north of Tasmania, Australia.It is located on the north western part of the city . It is the location of the Cataract Gorge and the Trevallyn Dam...
  
  , Launceston
  Launceston, Tasmania
  Launceston is a city in the north of the state of Tasmania, Australia at the junction of the North Esk and South Esk rivers where they become the Tamar River. Launceston is the second largest city in Tasmania after the state capital Hobart...
  
  , Tasmania
  Tasmania
  Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
  
  
• Purdon & Featherstone, Battery point, Hobart
  Hobart
  Hobart is the state capital and most populous city of the Australian island state of Tasmania. Founded in 1804 as a penal colony,Hobart is Australia's second oldest capital city after Sydney. In 2009, the city had a greater area population of approximately 212,019. A resident of Hobart is known as...
  
  , Tasmania
  Tasmania
  Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
  
  

United Kingdom

• Berthon Boat Co Ltd, Lymington
  Lymington
  Lymington is a port on the west bank of the Lymington River on the Solent, in the New Forest district of Hampshire, England. It is to the east of the South East Dorset conurbation, and faces Yarmouth on the Isle of Wight which is connected to it by a car ferry, operated by Wightlink. The town...
  
  
• M W Blackmore & Sons Ltd, Bideford
  Bideford
  Bideford is a small port town on the estuary of the River Torridge in north Devon, south-west England. It is also the main town of the Torridge local government district.-History:...
  
  
• G Bunn, Wroxham
  Wroxham
  Wroxham is a village and civil parish in the English county of Norfolk. The civil parish of Wroxham has an area of 6.21 square kilometres and in 2001 had a population of 1532 in 666 households. The village is situated within the Norfolk Broads on the south side of a loop in the middle reaches of...
  
  
• A H Moody & Sons, Swanick Shore
• R A Newman & Sons, Poole
  Poole
  Poole is a large coastal town and seaport in the county of Dorset, on the south coast of England. The town is east of Dorchester, and Bournemouth adjoins Poole to the east. The Borough of Poole was made a unitary authority in 1997, gaining administrative independence from Dorset County Council...
  
  
• Leo Robinson, Oulton Broad
  Oulton Broad
  Oulton Broad refers to both the lake and the suburb of Lowestoft in Suffolk, England located 2 miles west of the centre of the town.-Oulton Broad:...
  
  , Lowestoft
  Lowestoft
  Lowestoft is a town in the English county of Suffolk. The town is on the North Sea coast and is the most easterly point of the United Kingdom. It is north-east of London, north-east of Ipswich and south-east of Norwich...
  
  
• Anderson, Rigden & Perkins, Whitstable
  Whitstable
  Whitstable is a seaside town in Northeast Kent, Southeast England. It is approximately north of the city of Canterbury and approximately west of the seaside town of Herne Bay. It is part of the City of Canterbury district and has a population of about 30,000.Whitstable is famous for its oysters,...
  
  .
• Bolson, Poole, Dorset
  Dorset
  Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
  
  .
• Bute Slip, Clyde, Scotland
  Scotland
  Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
  
  .
• Elkins, Christchurch, Dorset
  Dorset
  Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
  
  .
• Harland & Wolff, Belfast, Northern Ireland
  Northern Ireland
  Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...
  
  .
• Hillyard, Littlehampton, West Sussex
  West Sussex
  West Sussex is a county in the south of England, bordering onto East Sussex , Hampshire and Surrey. The county of Sussex has been divided into East and West since the 12th century, and obtained separate county councils in 1888, but it remained a single ceremonial county until 1974 and the coming...
  
  .
• Lady Bee, Isleworth
  Isleworth
  Isleworth is a small town of Saxon origin sited within the London Borough of Hounslow in west London, England. It lies immediately east of the town of Hounslow and west of the River Thames and its tributary the River Crane. Isleworth's original area of settlement, alongside the Thames, is known as...
  
  .
• McGruer, Clynder, Scotland
  Scotland
  Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
  
  .
• McClean, Renfrew, Scotland
  Scotland
  Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
  
  .
• Morgan Giles, Teignmouth Devon
  Devon
  Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
  
  .
• Ranalagh Yacht Yard, Wooton, Isle of Wight
  Isle of Wight
  The Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...
  
  .
• Robinson, Tewkesbury, Gloucestershire
  Gloucestershire
  Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....
  
  .
• Sittingbourne Shipbuilding Co, Kent
  Kent
  Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
  
  .
• Sussex Shipbuilding Co, Shoreham-by-Sea
  Shoreham-by-Sea
  Shoreham-by-Sea is a small town, port and seaside resort in West Sussex, England. Shoreham-by-Sea railway station is located less than a mile from the town centre and London Gatwick Airport is away...
  
  .
• Thornycroft
  Thornycroft
  Thornycroft was a United Kingdom-based vehicle manufacturer which built coaches, buses, and trucks from 1896 until 1977.-History:Thornycroft started out with steam vans and lorries. John Isaac Thornycroft, the naval engineer, built his first steam lorry in 1896...
  
  , Hampton, London
  Hampton, London
  Hampton is a suburban area, centred on an old village on the north bank of the River Thames, in the London Borough of Richmond upon Thames in England. Formerly it was in the county of Middlesex, which was formerly also its postal county. The population is about 9,500...
  
  .
• Herbert Woods, Potter Heigham
  Potter Heigham
  Potter Heigham is a village and civil parish on the River Thurne in the English county of Norfolk. It is situated some north-east of the city of Norwich on the A149 road, and on The Broads....
  
  , Norfolk
  Norfolk
  Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...
  
  .

USA

• Ackerman Boat Works, Azusa, California
  Azusa, California
  Azusa is a city in Los Angeles County, California, United States. The population was 46,361 at the 2010 census, up from 44,712 at the 2000 census. Though sometimes assumed to be a compaction of the phrase "everything from A to Z in the USA" from an old Jack Benny joke, the place name "Azusa"...
  
  .
• Dodge, Newport News.
• Edgar, Rye, New York
  Rye (city), New York
  Rye is a city in Westchester County, New York, United States. It is separate from the town of Rye, which is larger than the city. Rye city, formerly the village of Rye, was part of the town until 1942, when it received its charter as a city, the most recent to be issued in New York...
  
  .

• Elscot, City Island, New York.
• Everett Marine Ways Inc, Everett, Washington
  Everett, Washington
  Everett is the county seat of and the largest city in Snohomish County, Washington, United States. Named for Everett Colby, son of founder Charles L. Colby, it lies north of Seattle. The city had a total population of 103,019 at the 2010 census, making it the 6th largest in the state and...
  
   (near Seattle)
• Freeport Shipyard, Long Island
  Long Island
  Long Island is an island located in the southeast part of the U.S. state of New York, just east of Manhattan. Stretching northeast into the Atlantic Ocean, Long Island contains four counties, two of which are boroughs of New York City , and two of which are mainly suburban...
  
  .
• Grays Harbour Shipbuilding Co, Aberdeen, Washington
  Aberdeen, Washington
  Aberdeen is a city in Grays Harbor County, Washington, United States, founded by Samuel Benn in 1884. Aberdeen was incorporated on May 12, 1890. The city is the economic center of Grays Harbor County, bordering the cities of Hoquiam and Cosmopolis...
  
  .
• Harris & Parsons, Greenwich, Rhode Island
  East Greenwich, Rhode Island
  East Greenwich is a town in and the county seat of Kent County, Rhode Island, United States. The population was 13,146 at the 2010 census. East Greenwich is the wealthiest municipality within the state of Rhode Island....
  
  
• Hiltebrant, Kingston, New York
  Kingston, New York
  Kingston is a city in and the county seat of Ulster County, New York, USA. It is north of New York City and south of Albany. It became New York's first capital in 1777, and was burned by the British Oct. 16, 1777, after the Battles of Saratoga...
  
  
• Huskins Yacht Corp.
• Chas. P. Leek, Lower Bank, New Jersey.
• Madden & Lewis, Sausalito
  Sausalito, California
  Sausalito is a San Francisco Bay Area city, in Marin County, California, United States. Sausalito is south-southeast of San Rafael, at an elevation of 13 feet . The population was 7,061 as of the 2010 census. The community is situated near the northern end of the Golden Gate Bridge, and prior to...
  
  , Marin Peninsula, California.
• Perkins & Vaughn, Wickford, Rhode Island
  Wickford, Rhode Island
  Wickford is a small village in the town of North Kingstown, Rhode Island, United States, which is named after Wickford in Essex, England. Wickford is located on the west side of Narragansett Bay, just about a 20 minute drive across two bridges from Newport, Rhode Island...
  
  
• Quincy Adams.
• Thorsen, Ellsworth, Maine
  Ellsworth, Maine
  Ellsworth is a city in and the county seat of Hancock County, Maine, United States. The 2010 Census determined it had a population of 7,741. Ellsworth was Maine's fastest growing city from 2000-2010 with a growth rate of nearly 20 percent...
  
  .
• Truscott, St. Joseph, Michigan
  St. Joseph, Michigan
  St. Joseph is a city in the US state of Michigan. It was incorporated as a village in 1834 and as a city in 1891. As of the 2000 census, the city population was 8,789. It lies on the shore of Lake Michigan, at the mouth of the St. Joseph River, about east-northeast of Chicago. It is the county...
  
  .

others

• Africa Marine, Mombasa
  Mombasa
  Mombasa is the second-largest city in Kenya. Lying next to the Indian Ocean, it has a major port and an international airport. The city also serves as the centre of the coastal tourism industry....
  
  .
• Alcock Ashdown, Karachi
  Karachi
  Karachi is the largest city, main seaport and the main financial centre of Pakistan, as well as the capital of the province of Sindh. The city has an estimated population of 13 to 15 million, while the total metropolitan area has a population of over 18 million...
  
  .
• Armedi Shipyard, Bombay.
• Bombay Dockyard.
• Bombay Steam Navigation.
• Garden Reach, Calcutta.
• Hooghly Dock & Eng. Calcutta.
• India General Navigation, Calcutta.
• Irrawadi Flotilla Co., Rangoon.
• Mohatta, Karachi.
• Nichol, Durban, South Africa
  South Africa
  The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
  
  .
• Pehara, Alexandria
  Alexandria
  Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...
  
  , Egypt
  Egypt
  Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
  
  .
• Rangoon Dockyard, Rangoon.
• Scindia, Bombay.
• Spadbrow, Durban
  Durban
  Durban is the largest city in the South African province of KwaZulu-Natal and the third largest city in South Africa. It forms part of the eThekwini metropolitan municipality. Durban is famous for being the busiest port in South Africa. It is also seen as one of the major centres of tourism...
  
  , South Africa
  South Africa
  The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
  
  .
• Thornycroft, Singapore
  Singapore
  Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...
  
  .
• Walker, Colombo
  Colombo
  Colombo is the largest city of Sri Lanka. It is located on the west coast of the island and adjacent to Sri Jayawardenapura Kotte, the capital of Sri Lanka. Colombo is often referred to as the capital of the country, since Sri Jayawardenapura Kotte is a satellite city of Colombo...
  
  , Ceylon.

See also

• Motor Launch
  Motor Launch
  A Motor Launch is a small military vessel in British navy service. It was designed for harbour defence and submarine chasing or for armed high speed air-sea rescue....
  
  
• Motor Gun Boat
  Motor Gun Boat
  Motor Gun Boat was a Royal Navy term for a small military vessel of the Second World War. They were physically similar to the Motor Torpedo Boats but equipped with a mix of guns instead of torpedoes. Their small size and high speed made them difficult targets for E-boats or torpedo bombers, but...
  
  
• Motor Torpedo Boat
  Motor Torpedo Boat
  Motor Torpedo Boat was the name given to fast torpedo boats by the Royal Navy, and the Royal Canadian Navy.The capitalised term is generally used for the Royal Navy boats and abbreviated to "MTB"...
  
  
• Submarine chaser
  Submarine chaser
  A submarine chaser is a small and fast naval vessel specially intended for anti-submarine warfare. Although similar vessels were designed and used by many nations, this designation was most famously used by ships built by the United States of America...
  
  
• National Historic Ships (many surviving HDMLs in British waters are on its register.)
• British Coastal Forces of World War II

External links

• The history of The Royal Naval Patrol Service
• HDML 1301 today
• HDML 1301 ~ Operation Brassard - 17 Jun 1944
• HM HDML 1001 her Royal Navy and subsequent career
• Personal account of life aboard HDML 1383
• Enter HDML or Harbour Defence Motor Launch into search box of BBC's WW2 Peoples' War for more individual accounts.
• HDML 1387 later HMS Medusa at National Historic Ships Register