During the First World War, Carline served on the Western Front and in the Middle East, where he travelled extensively through Palestine, Syria, India and modern day Iran and Iraq.

[5][6] During the First World War, Carline joined the Middlesex Regiment of the British army in 1916, before transferring to the Royal Flying Corps, RFC, in 1917.

From September 1917 until the spring of 1918 he was employed by the Air Ministry to paint large surveys of the front lines in France onto canvas, for which he established a studio close to the family home in Hampstead.

In several of his aerial paintings, Carline showed the influence of the Cubist artworks he had seen in Paris before the war as he adopted unconventional perspectives to depict the ground below as two-dimensional and abstracted.

[10] The brothers stayed in Cairo before moving to Baghdad where they remained until the middle of July when they went to Mosul from where the RAF were planning bombing raids against the Kurdish uprising.

The Carline family home in Hampstead became the centre of an artistic circle that included Henry Lamb, Stanley Spencer, Mark Gertler and John Nash.

[12] In 1935, with Michael Sadler, Carline wrote a book entitled Arts of West Africa and organized an accompanying exhibition on the subject.

Carline was active in the Artists' International Association and during 1937 and 1938 he spent time in Mexico and the United States on their behalf supporting various arts' projects.