Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
DRAWBRIDGE
As described in historical dictionaries
Patronymica Britannica (1860)
DRAWBRIDGE. First imposed upon a retainer in a fortified house whose duty it was to superintend the drawbridge. Harry o' the Drawbridge would be a 'ery likely appellation for such a guardsi#in.