Question: Which world war did Ronald Wallens participate in?

Context paragraphs:
HMS Bagshot (J57): HMS "Bagshot" was a Hunt-class minesweeper of the "Aberdare" sub-class built for the Royal Navy during World War I.  She was not completed in time to participate in the First World War and survived the Second World War to be sold for scrap in 1947.

Royal Air Force: The Royal Air Force (RAF) is the United Kingdom's aerial warfare force.  Formed towards the end of the First World War on 1 April 1918, it is the oldest independent air force in the world.  Following victory over the Central Powers in 1918 the RAF emerged as, at the time, the largest air force in the world.  Since its formation, the RAF has taken a significant role in British military history, in particular, playing a large part in the Second World War where it fought its most famous campaign, the Battle of Britain.

Alfred Anderson (veteran): Alfred Anderson (25 June 1896 – 21 November 2005) was a Scottish joiner and veteran of the First World War.  He was the last known holder of the 1914 Star (the Old Contemptibles), the last known combatant to participate in the 1914 World War I Christmas truce, Scotland's last known World War I veteran, and Scotland's oldest man for more than a year.

History of the Scotland national football team: The history of the Scotland national football team dates back to the first ever international football match in 1872.  Until the Second World War, Scotland mainly competed against the other Home Nations in the British Home Championship, with the most keenly contested fixture being the match with England.  The Scottish Football Association, which governs the team, joined the international governing body FIFA in 1910, but along with the other Home Nations withdrew from FIFA in 1928.  This meant that Scotland did not participate in the World Cups of 1930, 1934 or 1938.  The Home Nations rejoined FIFA after the Second World War and Scotland then started to participate in international competitions.  Scotland have since participated in eight World Cups and two European Championship tournaments, but have never progressed beyond the first stage.  Scotland have not qualified for a tournament since the 1998 World Cup.

HMS Saltash (J62): HMS "Saltash" (J62) was a Hunt-class minesweeper of the "Aberdare" sub-class built for the Royal Navy during World War I.  She was not finished in time to participate in the First World War and survived the Second World War to be sold for scrap in 1947.

Ronald Wallens: Ronald Walter "Wally" Wallens, DFC (1 February 1916 – 13 November 1995) was a Royal Air Force officer, who flew during the Battle of Britain and as such is one of "The Few".

HMS Albury (J41): HMS "Albury" was a Hunt-class minesweeper of the "Aberdare" sub-class built for the Royal Navy during World War I.  She was not finished in time to participate in the First World War and survived the Second World War to be sold for scrap in 1947.

HMS Alresford (J06): HMS "Alresford" was a Hunt-class minesweeper of the "Aberdare" sub-class built for the Royal Navy during World War I.  She was not finished in time to participate in the First World War and survived the Second World War to be sold for scrap in 1947.

David Dunbar (actor): David Dunbar (14 September 1886 – 7 November 1953) was an Australian film actor.  Dunbar was a prominent actor in American and British silent films, particularly in westerns, but switched to playing more minor roles after the arrival of sound.  In later years he appeared mostly in British-themed Hollywood films.  He was one of the first film actors beginning his screen career with Pathe Freres, Paris in 1910.  Previously he was an actor on the legitimate stage both in Australia, his homeland and in Britain.  On 7 March 1926 his wife Blanche was killed in a car collision in the Hollywood Hills.  He had one sister, Miriam Kathleen (Strachan) Dunbar who remained in Petersham, New South Wales.  Miriam married William Thomas Strachan, the children of that marriage being Miriam Kathleen and William James Strachan.  William James (Bill) returned from the Second World War to Australia and settled with his wife Barbara (Grant) Strachan in Sydney and later in Melbourne, Victoria, bringing up three children, Susan Marion, William Grant and Scott James Strachan.  The Strachan family included Graeme Ronald (Shirley) Strachan, a media personality and lead singer of the 1970s rock group "Skyhooks".  Miriam Kathleen married Ronald George Fordham, who perished as a prisoner of war in Malaya during the Second World War.  Miriam Kathleen died in 1944, leaving Brian Ronald and Joan Fordham.

HMS Derby (J90): HMS "Derby" was a Hunt-class minesweeper of the "Aberdare" sub-class built for the Royal Navy during World War I.  She was not finished in time to participate in the First World War and survived the Second World War to be sold for scrap in 1946.

Supporting paragraphs: Ronald Wallens Royal Air Force
Answer: the Second World War