USS O-4 (SS-65) was one of 16 O-class submarines built for the United States Navy during World War I.

The O-class submarines were designed to meet a Navy requirement for coastal defense boats.

[2] For surface running, the boats were powered by two 440-brake-horsepower (328 kW) diesel engines, each driving one propeller shaft.

O-4 operated out of Philadelphia, Pennsylvania, during World War I and patrolled the U.S. Atlantic coast from Cape Cod to Key West, Florida.

O-4 held the distinction of being the US Navy submarine in service for the longest period of time (27 years 4 months) until surpassed by USS Picuda in February 1971.