The SS United States Conservancy said it reported the break-in at "America's Flagship."
Police say burglars stole several batteries and tools, causing damage to the property.
No arrests have been made, police say. It wasn't immediately known when the burglary occurred.
The conservancy said it wouldn't have any additional comment as the investigation continues.
Anyone with information can call or text police at 215-686-TIPS (8477).
This incident comes just days after Okaloosa County, Florida inked a tentative deal to turn the ship into the world's largest artificial reef.
The contract approved Tuesday by officials in Florida's coastal panhandle is contingent upon the resolution of court-imposed mediation, after a judge ordered the storied ship to vacate its berth, following a yearslong dispute over rent and dockage fees.
The largest passenger ship ever built in the U.S., the SS United States shattered a record for the fastest transatlantic crossing by a passenger liner on its maiden voyage in 1952, The Associated Press reported from aboard the vessel.
The deal to buy the ship, which officials said could cost more than $10 million, could close in a matter of weeks, pending court mediation. The lengthy process of cleaning, transporting and sinking the vessel is expected to take at least 1.5 years.
WATCH: Action News archive - SS United States towed under Philadelphia's Walt Whitman Bridge
Action News archive: Does the SS United States fit under Philadelphia's Walt Whitman Bridge?
Christened in 1952, the 1,000-foot ocean liner was once considered a beacon of American engineering, doubling as a military vessel that could carry thousands of troops. On its maiden voyage in 1952, it shattered the transatlantic speed record in both directions, when it reached an average speed of 36 knots, or just over 41 mph (66 kph), The Associated Press reported from aboard the ship.
On that voyage, the ship crossed the Atlantic in three days, 10 hours and 40 minutes, besting the RMS Queen Mary's time by 10 hours. To this day, the SS United States holds the transatlantic speed record for an ocean liner.
It became a reserve ship in 1969 and later bounced to various private owners who hoped to redevelop it but eventually found their plans to be too expensive or poorly timed.
The massive ocean liner first appeared in Philadelphia in July 1996. For roughly two weeks, the 1,000-foot vessel was parked along the Delaware River, next to the Walt Whitman Bridge.
The size of the ship and its proximity to the important Philadelphia bridge made bridge officials nervous that it was too close - so they ordered that it be moved to a more fitting location.
WATCH: Action News archive: SS United States ordered to move away from Philadelphia's Walt Whitman Bridge
Action News archive: SS United States ordered to move away from Philadelphia's Walt Whitman Bridge
Then, on July 25, 1996, a team of tugboats led the mission of nudging the behemoth into the middle of the Delaware River before towing it upstream and carefully under the Walt Whitman. That temporary spot turned into a nearly 30-year stay.
The Associated Press contributed to this report.