Percy Mack enlisted in the U.S. Marine Corp for a 4 year enlistment on 2 Oct 1911 in Philadelphia, PA giving his place of birth as New York, NY and his date of birth as 12 Aug 1982, occupation bookeeper, and residence 207 E. 13 Street. He gave his next of kin as his grandfather, James P. Cassidy, Los Angeles, CA. Since he was underage, a guardian had to be appointed. Herbert Van Dyke, Investments S. Park Row, New York, swore that "to the best of my knowledge and belief he ‏(percy M. Cassidy)‏ was born in New York, NY on 12 Aug 1892 and had no other legal guardian." He served Marine Navy Yard, Philadelhpia, PA, 2 Oct 1011 - 4 Jan 1912; Marine Barracks, Annapolis, MD, 4 Jan 1912 -14 Mar 1912; USS Idaho 12 Mar 1912 - 30 Oct 1913; Marine Barracks, Philadelphia, PA, 3 Nov 1913 - 26 Apr 1914. Embarked onboard USS New York at Tompkinsville, NY 26 Apr 1914 and disembarked at Fort San Juan de Uiloa, Vera Cruz, Mexico 15 Jun 1914. Embarked USS Washington 22 Jun 1914 - 2 Jan 1915; Marine Barracks, Portsmouth, NH 2 Jan 1915 - 11 Jan 1915; Marine Barracks, Philadelphia, PA 13 Jan 1915 - 1 Jul 1915; Marine Barracks, Boston, MA, 1 Jul 1915 - 16 Sep 1915. Honerable Discharge Serial 156534. Received the Good Conduct Medal. Re-enlisted 5 Jun 1917 as a Private in New York, NY listing his address as 24 E. 23 Street New York, NY and his former address as 39 Linden Street, Chicopee, MA and his next of kin as Mrs. F. Barker ‏(r 223)‏, 81 Haverkall Street, Lawrence, MA. Served Marine Barracks, Boston Navy Yard 30 Jun 1917 - 13 Aug 1917; Assistant Paymasters Office US Marine Corp, New York, NY 14 Aug 1917 - 31 Oct 1919. Honerable discharge convenience of the government 31 Oct 1919. Rank Corporal. Re-enlisted 14 Nov 1919 for a two year enlistment showing his wife, Marion Cassidy, as next of kin at 215 Crescent Street, Long Island City. Served Assistant Paymaster US Marine Corp, New York, NY 14 Nov 1919 - 30 Nov 1920; Office of Assistant Paymaster, 1415 Locust Street, Philadelphia, PA 1 Dec 1920 - 9 Sep 1921; Marine Corp Recruiting 10 Sep 1921 - 10 May 1922. Enlistment was extended for one year. Attained rank of QM SGT. ‏(Copy of service records in posession of Patricia K. Cassidy.)‏

The National Archives letter of 18 May 1999, in answer to a request from Patricia Cassidy, worte the following: "USS Idaho from Mar 1912 to Oct 1913 was at Philadelphia Navy Yard; Tampico, Mexico; Newport, RI; Portland, ME; Portsmouth, NH; Rockland, ME; Newport, RI; Hampton Roads, VA; Philadelphia Navy Yard; Hampton Roads, The USS New York between Apr 1914 to Jun 1914 was at the Brooklyn Navy Yard; Vera Cruz, Mexico. The USS Washington between Jun 1914 to Dec 1914 was at Puerto Plata, San Domingo; Guantanano, Cuba; Vera Cruz, Mexico; Cape Haitian, Haiti; Puerto Plata; Santo Domingo City, DR; Philadelphia Navy Yard; Portsmouth, NH."

Percy Mack worked for Westinghouse Northeastern Region Marine Division 1922 - retirement 1 Sep 1957 Marine Division. His job required his entering the Brooklyn Navy Yard. When World War II came and proof of citizenship was required, Captain R.M. O'Tool wrote a letter confirming his place of birth as New York.

Percy is buried St. Charles Cemetery, Calverton, NY.