Maine, U.S., Military Index, 1917-1920: Ernest L. Oak, born at Skowhegan, residence Gardiner, serial number 3162447; inducted at Waterville on 25 July 1918, corporal on 20 November 1918, Co. A, 73rd Infantry, no overseas service, honorably discharged on demobilization 17 January 1919.
Image · dated 1918-07-25 to 1919-01-17 · source: Ancestry.com, Maine, U.S., Military Index, 1917-1920 (original data: Roster of Maine in the Military Service of the U.S. and Allies in World War, Augusta, 1929)

How it is shown: Displayed as a crop of the Detail (and Source) table only: the title bar, the Save and share controls and the page header are cropped out.
Keep in mind: What the page says: Confirmed: 'Ind: Waterville, Kennebec Co. No. 2, July 25/18. Cpl Nov. 20/18. Org: Co A 73 Inf to disch. Overseas service: None. Hon disch on demob: Jan. 17, 1919.' The birth date given is 5 Jan 1894, where his draft card and headstone give 5 June 1894; this looks like a slip in the roster or its indexing. 'Ind' is read here as inducted; the abbreviation is not spelled out on the page, and the entry does not name the Army branch beyond the 73rd Infantry. Whether this is our person: Confirmed: the Skowhegan birthplace, the Gardiner residence, Co. A 73rd Infantry and the 17 January 1919 date agree with his headstone and the Veterans Administration index; only the birth month differs.