Moselli, who had been in the Merchant Navy before he began his writing career in 1910, and he returned to the sea during the war. The only information I have (a reprint of two articles by Georges Fronval, a fellow pulp writer) says that he commanded a troop transport taking French troops from Marseilles to Salonika in Greece. The Salonika Front, also known as the Macedonian front, was the result of an attempt by the Allied Powers to aid Serbia, in the autumn of 1915. It remained an active front until September 1918, when Bulgaria capitulated and Serbia was liberated.
José Moselli in the Great War