His WWI Draft Card (June 5, 1917) asked what previous military service he had, and he reported that he had served for three years as a private in the Calvary in New York. I recently learned about his service!
This image is from a newly posted database at Ancestry.com: New York Mexican Punitive Campaign Muster Rolls for National Guard, 1916-1917.
Below I have done my best to transcribe the document, with the handwritten entries in blue. If anyone has thoughts on some of the handwriting under remarks, please let me know.
Pyle, Charles McAlpin
Date of Commission or Enlistment in State Service: 27 April 1914
Home Station or Company Rendezvous: Van Cortlandt Park
Mustered: 30 June 1916, Grade: Pvt; Company: C; Regiment: Sq A. Cav.
Left the Organization:
How: M.O. [Mustered Out?] When: 28 Dec 1916; Grade: 1C Pvt.; Explanation: With Troops at N.Y. City
Remarks: dropped for removal 5/29/16. S.O. 64 Sq. A.: taken up 6/23/16. S.O.I 08. Sqr. A.
Sick in qrs. in ll[?] Oct 4/16. A.W.O.L. July 9-12/16
Aptd 1 Class pvt from pvt. Aug 1/16 O-12
Age: 22 years; height 5 feet 9 inches; complexion light; eyes hazel; hair brown;
born Morristown N.J.; occupation business; residence Morristown N.J.;
68 William St., N.Y. City; relationship brother.
Although the title of this database references the Mexican Punitive Campaign, I believe my grandfather remained in New York. Two reasons: one is that the explanation in the above document indicates: "With Troops at N.Y. City," and two, there is no family story about my grandfather going to Texas to patrol the Mexican border.
The National Archives has two articles about the Mexican Punitive Campaign Part 1 here and Part 2 here.