| Year | Date | Historical Events |
| 1938 | Jun 20 | Keel laid down by the Electric Boat Co., Groton, CT. |
| 1939 | May 25 | Launched. |
| | Nov 27 | Commissioned with LT. J.K. Morrison Jr., in command. Following shakedown, Sealion, assigned to Submarine Division 17, prepared for overseas deployment.
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| 1940 | Apr 1 | Sealion sailed with her division for the Philippine Islands, arriving at Cavite in the fall to commence operations as a unit of the Asiatic Fleet. |
| | Apr 1 | (Cont'd.) Into October 1941, she ranged from Luzon into the Sulu Archipelago, then, with another submarine of her division, now SubDiv 202, she prepared for a regular overhaul at the Cavite Navy Yard. |
| 1941 | Dec 8 | Sealion began her yard overhaul. |
| | Dec 10 | Sealion took 2 direct hits from a Japanese aerial attack at the Cavite Navy Yard in the Phillipines and sank alongside the pier. 4 men who were working in the after engine room were killed. |
| | Dec 10 | (Cont'd.) Sealion flooded immediately and settled down by the stern with 40% of her main deck underwater and a 15 degree list to starboard. |
| | Dec 25 | The destruction of the Navy Yard made repairs impossible, and Sealion was ordered destroyed. All salvagable equipment was taken off, depth charges were placed inside, and the explosives were set off to prevent her from being made useful to the enemy.
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