On January 8th, 1916, Hattie May Mastin joined the Army Medical Corps in Kingston, Ontario as a nursing sister. She was born on July 31st, 1888 in Deseronto, the daughter of Melbourne Mastin and Minerva Jane (née Bruin). Hattie had served in the military hospital in Belleville for seven weeks. She was living at 268 William Street, Belleville when she joined the army. Hattie was the first woman to enlist of the people from Deseronto who served in the war, one of only two in total.
In 1921, Hattie was back with her mother and siblings, living at 234 John Street, Belleville.