At the beginning of the Second World War Rosoman joined the Auxiliary Fire Service, which in 1941 became the National Fire Service, and began making paintings based on his experiences as a fire-fighter during the Battle of Britain and the Blitz in London.
One of these A House Collapsing on Two Firemen, Shoe Lane, London, EC4 (1941), now in the Imperial War Museum, shows the incident on the night of 29/30 December 1940 in which a young fireman who had just relieved Rosoman at his position was killed by a collapsing building in the City of London.
Whilst the other fireman, the author William Sansom, survived, the scene haunted Rosoman and he re-worked the painting several times.
Rosoman sometimes called his work, The Falling Wall.
 It was completed in August 1941.
The painting was shown in the Firemen Artists exhibition at the Royal Academy in 1941.
 
A number of artists had joined the NFS and an firemen artists' committee had been formed which included Bernard Hailstone, Paul Lucien Dessau, Norman Hepple and Robert Coram as well as Rosoman.
As well as contributing to both War Artists' Advisory Committee, WAAC, and specialist civil defence art shows, the firemen held several of their own exhibitions.

In 1943 Rosoman was seconded to the War Office to illustrate books on fire-fighting, and in April 1945 was appointed, by the War Artists' Advisory Committee, to a full-time salaried position, along with James Morris, to document the activities of the British Pacific Fleet.
Commissioned as a captain in the Royal Marines, he was posted to the Far East.
He joined the aircraft carrier HMS Formidable in Sydney in May 1945 and sailed with her for three months before returning to Sydney to work his on-board sketches into finished paintings.
On board Formidable he became fascinated by the new technologies he encountered there, "I've become interested in all sorts of strange devices like radar indicators, pom-poms and planes with wings that fold up like a moth's".
He travelled to Hong Kong in September 1945 to record bomb damage and although he reached the coast of Japan he did not go ashore there.
At the beginning of the Second World War Rosoman joined the Auxiliary Fire Service, which in 1941 became the National Fire Service, and began making paintings based on his experiences as a fire-fighter during the Battle of Britain and the Blitz in London. One of these A House Collapsing on Two Firemen, Shoe Lane, London, EC4 (1941), now in the Imperial War Museum, shows the incident on the night of 29/30 December 1940 in which a young fireman who had just relieved Rosoman at his position was killed by a collapsing building in the City of London. Whilst the other fireman, the author William Sansom, survived, the scene haunted Rosoman and he re-worked the painting several times. Rosoman sometimes called his work, The Falling Wall.  It was completed in August 1941. The painting was shown in the Firemen Artists exhibition at the Royal Academy in 1941.  
A number of artists had joined the NFS and an firemen artists' committee had been formed which included Bernard Hailstone, Paul Lucien Dessau, Norman Hepple and Robert Coram as well as Rosoman. As well as contributing to both War Artists' Advisory Committee, WAAC, and specialist civil defence art shows, the firemen held several of their own exhibitions.
In 1943 Rosoman was seconded to the War Office to illustrate books on fire-fighting, and in April 1945 was appointed, by the War Artists' Advisory Committee, to a full-time salaried position, along with James Morris, to document the activities of the British Pacific Fleet. Commissioned as a captain in the Royal Marines, he was posted to the Far East. He joined the aircraft carrier HMS Formidable in Sydney in May 1945 and sailed with her for three months before returning to Sydney to work his on-board sketches into finished paintings. On board Formidable he became fascinated by the new technologies he encountered there, "I've become interested in all sorts of strange devices like radar indicators, pom-poms and planes with wings that fold up like a moth's". He travelled to Hong Kong in September 1945 to record bomb damage and although he reached the coast of Japan he did not go ashore there.
Leonard Rosoman