Chailey Parish Magazine notes that a J Walder was serving with the Royal Engineers from January 1918 until the end of the war.
This could be Jesse Walder (born 1886 in Hove) or James Walder (born 1891 in Chailey); both of them brothers of Lewis Walder and the sons of Lewis and Emily Walder, latterly of Lane End Farm, Chailey. Or it could be John Walder, the son of George and Harriet Walder (nee Heasman) of South Street
Chailey Parish Magazine simply mentions Walder, Pioneer J, R E in its January 1918 issue and then repeats this information up to and including the final published roll call in July 1919.