 Hjort's task was to oversee the planning and construction of the Pennsylvania Railroads Tunnels under the Hudson River, and the Long Island Rail Road Tunnels under the East River.This was one of the greatest engineering and construction enterprises ever undertaken anywhere in the world up to that time.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.