(SS65: dp. 520.6 (surf. n.), 629 (subm.); l 1724; b. 18 Ό; dr. 145; s. 14 k. (surf.), 10.5 k. (subm.); cpl. 29; a. 1 3, 4 18 tt.; cl. O1).
O4, was laid down 4 December 1916 by the Fore River Shipbuilding Co., Quincy, Mass.; launched 20 October 1917; and commissioned 29 May 1918, Lt. R. H. English, in command.
O4 operated out of Philadelphia during World War I and patrolled the U.S. Atlantic coast from Cape Cod to Key West. On 24 July 1918, a British steamer mistook O4 and O6 for German U-boats and fired on the submarines. Although O4 received 6 hits from the steamer, she suffered no major damage. In November, she joined the 20-sub contingent that departed Newport the 3d for European waters; however, hostilities ceased before the boats had reached the Azores.
O4 then sailed to New London to train students at the submarine school there. Reclassified to a second line submarine 26 July 1924, and reverting to a first liner 6 June 1928, she trained Submarine School students at New London until 1931, with the exception of a brief tour at Coco Solo. O4 decommissioned 3 June 1931.
The approach of World War II saw the recall of O4 to active service. She recommissioned 29 January 1941 and trained students at the sub school until wars end. After the war, she steamed to Portsmouth, N.H., to decommission there 20 September 1945. She was struck from the Navy Register 11 October 1945, and scrapped 1 February 1946.