The British L-class submarine was originally planned under the emergency war programme as an improved version of the British E-class submarine.
 The scale of change allowed the L class to become a separate class.
HMS "L27" was a L-class submarine built for the Royal Navy during World War I.
 The boat was not completed before the end of the war and was one of three L-class boats to serve during World War II.
 She served as training boat before being broken up in 1944.
HMS "L23" was a L-class submarine built for the Royal Navy during World War I.
 The boat was not completed before the end of the war and was one of three L-class boats to serve during World War II.
 "L23" was sold for scrap in 1946.
Type L submarine may refer to one of the following classes of submarines based on the British L-class submarine :
The Leninets or L class were the second class of submarines to be built for the Soviet Navy.
 They were minelaying submarines and were based on the British L-class submarine, HMS "L55" , which was sunk during the British intervention in the Russian Civil War.
 Some experience from the previous "Dekabrist"-class submarine s was also utilised.
 The boats were of the saddle tank type and mines were carried in two stern galleries as pioneered on the pre-war "Krab" , the world's first minelaying submarine.
 These boats were considered successful by the Soviets and 25 were built in four groups between 1931 and 1941.
 Groups 3 and 4 had more powerful engines and higher speed.
HMS "L33" was a British L-class submarine built by Swan Hunter, Wallsend.
 She was launched on 29 May 1919 and was commissioned on an unknown date.
 She was armed with six torpedo tubes
The Yugoslav submarine "Hrabri" was the first of the "Hrabri"-class diesel-electric submarines built by the Vickers-Armstrong Naval Yard on the River Tyne in the United Kingdom, for the Kingdom of Serbs, Croats and Slovenes (later Yugoslavia).
 Launched in 1927, her design was based on that of the British L-class submarine of World War I, and she was built using parts originally assembled for a submarine of that class which was never completed.
 She was armed with six bow-mounted 533 mm torpedo tubes, two 102 mm guns and one machine gun, and could dive to 60 m .
The Yugoslav submarine "Nebojša" was the second of the "Hrabri"-class diesel-electric submarines built by the Vickers-Armstrong Naval Yard on the River Tyne in the United Kingdom, for the Kingdom of Serbs, Croats and Slovenes (later Yugoslavia) and was launched in 1927.
 Her design was based on that of the British L-class submarine of World War I, and she was built using parts originally assembled for a Royal Navy L-class submarine that was never built.
 She was armed with six bow-mounted 533 mm torpedo tubes, two 102 mm guns and one machine gun, and could dive to 60 m .
The British E class submarines started out as improved versions of the British D class submarine.
 The E class served with the Royal Navy throughout World War I as the backbone of the submarine fleet.
 The last surviving E class submarines were withdrawn from service by 1922.
The "Hrabri" class consisted of two submarines built by the Vickers-Armstrong Naval Yard, on the River Tyne, in the United Kingdom, for the Kingdom of Serbs, Croats and Slovenes (later Yugoslavia).
 Launched in 1927, the vessels were named "Hrabri" (Brave) and "Nebojša" (Fearless).
 Their design was based on that of the British L-class submarine of World War I, and they were built using parts originally assembled for L-class submarines that were never completed.
 The "Hrabri"-class were the first submarines to serve in the Royal Yugoslav Navy, and the class was joined by the two smaller French-made "Osvetnik"-class submarine s to make up the pre-war Yugoslav submarine force.
 They were armed with six bow-mounted 533 mm torpedo tubes, two 102 mm guns and one machine gun, and could dive to 60 m .

Question: The British L-class submarine is an improved version of a submarine that served throughout which war ?
Answer: World War I