Photo from NYC Water Flickr page
This custom modified vehicle was used to traverse lengths of the recently concrete lined Delaware Aqueduct in 1949. It served much the same inspection purpose as the original "Croton Maid", a custom made flat bottom boat used to inspect the interior of the Old Croton Aqueduct in 1842 before it was put into service. The Delaware Aqueduct is the newest NYC aqueduct, delivering water to NYC from the western Catskill Mountains. The last reservoir in the Delaware system was completed in the early 1960's.
NYC Water caption: "Inspection party photo op on the Delaware Aqueduct. On April 14, 1949, deputy Mayor John J. Bennett, Board of Water Supply President Irving V. A. Huie and engineer Joseph Heck showed how a remodeled car was driven for miles through the tunnel to check its condition after several years of emergency operation."