Until the entry of the United States into World War 1 the US military did not have a standard combat helmet. Initially US troops arriving in Europe were issued with the British Mk1 Brodie helmet or the French M15 Adrian helmets. The United States quickly started production of the British design, designated the M1917, for its own forces. Approximately 2.7 million of these were manufactured by the end of the war.
The M1917 was phased out of service soon after the end of the war due to its lack of protection from lateral fire and poor balance, and replaced with the more familiar M1 helmet. It is mainly due to the relative ease of construction (forging rather than casting) that this design remained in use by British and commonwealth forces until well after the Second World War.