In looking at a military headstone recently, I ran across the epitaph 119th Spruce Sq with World War I being the war listed on the headstone. I had to look Spruce Sq up as I had never seen the term on a V. A. headstone. It stands for Spruce Squadron. I went to Wikipedia and found https://en.wikipedia.org/wiki/List_of_American_aero_squadrons which has the sub-category of https://en.wikipedia.org/wiki/List_of_American_aero_squadrons#100th_to_149th_Aero_Squadrons. I found more information on this website – http://swansongrp.com/spruce_units.html.
The 119th Spruce was formed in August 1918 at Vancouver Barracks. In the same month they were sent to Joyce, Washington. Joyce, as well as a post office specially opened at Siemscary, were the main centers of operation of a major railroad construction project to reach the huge stands of spruce near the area currently bounded by Olympic National Park. This project involved over 3,000 soldiers located at many camps within Clallam County.
This Squadron formed a Military Police Detachment, the only unit of its type in the Spruce Production Division. This Police group was formed when it became necessary to control the soldiers enjoying their time off in the town of Port Angeles, Washington.
In August 1918, this Squadron was assigned to the lumber mill owned by the Puget Sound Mills and Timber Co., Port Angeles, Washington. In December 1918, the unit was moved to Vancouver Barracks and were demobilized there in January 1919.
The Washington spruce unit charts that I show on my website indicate that this unit had 5 officers and 222 enlisted men.
Another good source was this PDF: https://www.nps.gov/fova/learn/historyculture/upload/Tonsfeldt-SPD-Study-2013-2.pdf.