Born in Liverpool, England, in January 1890, Duncan had a normal childhood. At age 15, he first embarked on a sailing ship as an apprentice officer. In 1911, he obtained his officer's certificate and in 1912, he served aboard the RMS Baltic of the White Star Line. He briefly served on the Olympic in mid-1914, and in December 1915, he embarked on the new Olympic-class ship, the HMHS Britannic, as sixth officer until August 1916. When the Britannic returned to the White Star Line, this led to a voyage as an officer on the RMS Adriatic. However, in September 1916, he returned to the Britannic, now holding the position of fourth officer, and on November 12, 1916, he embarked again for another voyage towards Moudros.