Experts hope the sub will pinpoint at least three major breaks in the Delaware Aqueduct that could be leaking as much as 1.2 billion gallons of water each month. The aqueduct carries about 890 million gallons each day from reservoirs in the Catskill Mountains – about 70 percent of the supply for the city and parts of Westchester and Putnam counties.

The sub, called Ulysses and built at the Woods Hole Oceanographic Institution in Massachusetts, cost $2.4 million. It was lowered into position through an inspection shaft in Wawarsing in Ulster Country, near the Roundout Reservoir, and was expected to emerge sometime the next day in Kent, 45 miles away in Putnam County.

John McCarthy of the Malcolm Pirnie engineering firm overseeing the project said a preliminary analysis could be ready in two weeks, but three months will be needed to make a full report. Officials with the city’s Department of Environmental Protection said the sub was required because the breaks in the aqueduct might be so large that only the water pressure is preventing a collapse.

The submarine is equipped with sonar to keep it from hitting the walls of the 131⁄2-foot-wide aqueduct.