After the completion of these projects, Hjort was engaged with the Degnon Contracting Company of New York City, in the task of building part of the Catskill Water Supply Project, which was used to supply New York City with water. In 1911, Hjort went to Flinn-O'Rourke Construction Company and served as this firm's chief engineer from 1929 until his death in New York during 1944. Under his watch a string of New York City Subway tunnel projects were planned and completed, most notably the Brooklyn–Battery Tunnel between the southern tip of Manhattan and Brooklyn.