Question: The Charlton Automatic Rifle was to act as a substitute for what First World War-era light machine gun of US design?
Context: The RPK ("Ruchnoy Pulemyot Kalashnikova", Russian: "Ручной пулемёт Калашникова" or "Kalashnikov hand-held machine gun") is a 7.62×39mm light machine gun of Soviet design, developed by Mikhail Kalashnikov in the late 1950s, parallel with the AKM assault rifle.  It was created as part of a program designed to standardize the small arms inventory of the Red Army, where it replaced the 7.62×39mm RPD light machine gun.  The RPK continues to be used by the armed forces of countries of the former Soviet Union and certain African and Asian nations.  The RPK was also manufactured in Bulgaria and Romania. The Kk 62 , also known as Kvkk 62 (konekivääri 62 "machine gun 62" or kevyt konekivääri 62 "light machine gun 62") is a Finnish 7.62×39mm light machine gun designed in late 1950s with the first prototype ready for testing in 1960.  It was officially adopted as the standard infantry support weapon of the Finnish Defence Forces (FDF) in 1962 as the 7.62 "konekivääri" 62; the first weapons were delivered in 1966.  It remains in service, although a replacement has already entered use, namely the PKM general-purpose machine gun.  The weapon is known for its unreliability and is highly unpopular among Finnish conscripts. The 7.62×45mm (designated as the 7,62 × 45 by the C.I.P.) is a rimless bottlenecked intermediate rifle cartridge developed in Czechoslovakia.  It is fired by the Czech vz.  52 rifle, Vz.  52 machine gun and ZB-530 light machine gun.  The round was later dropped from use when the Czech converted to the standard Warsaw Pact round, the 7.62×39mm (fired by vz.  52/57 rifle and vz.  52/57 light machine gun).  Its muzzle velocity and muzzle energy are slightly higher than that of the 7.62×39mm cartridge. The Dror light machine gun (Hebrew for "Sparrow") was an Israeli light machine gun based on the M1941 Johnson light machine gun. The Chauchat, named after Colonel Louis Chauchat, the main contributor to its design, was the standard machine rifle or light machine gun of the French Army during World War I (1914–18).  Its official designation was "Fusil Mitrailleur Modele 1915 CSRG" (in English: ""Machine Rifle Model 1915 CSRG"").  Beginning in June 1916, it was placed into regular service with French infantry, where the troops called it the FM Chauchat.  The Chauchat machine rifle in 8mm Lebel was also extensively used in 1917–18 by the American Expeditionary Forces (A.E.F), where it was officially designated as the "Automatic Rifle, Model 1915 (Chauchat)".  A total of 262,000 Chauchat machine rifles were manufactured between December 1915 and November 1918, including 244,000 chambered for the 8mm Lebel service cartridge, making it the most widely manufactured automatic weapon of World War I.  The armies of eight other nations – Belgium, Finland, Greece, Italy, Poland, Romania, Russia, and Serbia – also used the Chauchat machine rifle in fairly large numbers during and after World War I. The Lewis gun (or Lewis automatic machine gun or Lewis automatic rifle) is a First World War-era light machine gun of US design that was perfected and mass-produced in the United Kingdom, and widely used by British and British Empire troops during the war.  With its distinctive barrel cooling shroud and top-mounted pan magazine, the Lewis served to the end of the Korean War.  It was also widely used as an aircraft machine gun, almost always with the cooling shroud removed, during both world wars. The ZB vz.  26 was a Czechoslovak light machine gun developed in the 1920s, which went on to enter service with several countries.  It saw its major use during World War II, and spawned the related ZB vz.  27, vz.  30, and vz.  33.  The ZB vz.  26 influenced many other light machine gun designs including the Bren light machine gun and the Type 96 Light Machine Gun.  The ZB-26 is famous for its reliability, simple components, quick-change barrel and ease of manufacturing. The Charlton Automatic Rifle was a fully automatic conversion of the Lee–Enfield rifle, designed by New Zealander Philip Charlton in 1941 to act as a substitute for the Bren and Lewis gun light machine guns which were in chronically short supply at the time. The M249 light machine gun (LMG), formerly designated the M249 Squad Automatic Weapon (SAW) and formally written as Light Machine Gun, 5.56 mm, M249, is the American adaptation of the Belgian FN Minimi, a light machine gun manufactured by the Belgian company FN Herstal (FN).  The M249 is manufactured in the United States by the local subsidiary FN Manufacturing LLC in South Carolina and is widely used in the U.S. Armed Forces.  The weapon was introduced in 1984 after being judged the most effective of a number of candidate weapons to address the lack of automatic firepower in small units.  The M249 provides infantry squads with the high rate of fire of a machine gun combined with accuracy and portability approaching that of a rifle. The Rieder Automatic Rifle was a fully automatic Lee–Enfield SMLE rifle conversion of South African origin.  The Rieder device could be installed quickly with the use of simple tools.  A similar weapon of New Zealand origin was the Charlton Automatic Rifle.
Answer: Lewis gun