Green’s Dictionary of Slang

(US) an infantryman.

1867		B.W. Duke Hist. Morgan’s Cavalry 400: When the ‘webfeet’ called us ‘buttermilk rangers’, we did not get angry with them [OED].
1882		(con. 1861-5) S.R. Watkins Co. Aytch 4: An humble private in the rear rank in an infantry regiment, commonly called a ‘webfoot’.