How long did it take to build these submarines?
In the period between the two world wars, it could take as much as two to three years to complete a submarine. There was little urgency and we were likely making changes to the designs as we learned more about how prior boats performed. There was also some incentive to take longer in order to improve planning and to maintain staffing levels in the shipyards. However, by the late 1930s, as the war was on the horizon and more boats were being ordered, the typical time to complete a submarine was down to about a year and a half.
When the war had broken out in Europe, contracts were being let to begin building ships to either as an effort to keep us out of the war or to be able to fight it effectively. Construction had already begun, but not on a pace that would soon be needed.
By the time we were in the war, in December of 1941, construction had continued to speed up. Submarine designs had been frozen and soon shipyards were operating 24 hours per day, seven days per week. Shipyards would also have multiple boats under construction at any one time. There would be some boats where the work had just begun and others farther along but still in drydocks. Others may have been launched but still needed a few a few months for more work to be completed. During the war, boats would usually be commissioned less than a year after construction began.
For example, construction on the Pampanito began on March 15, 1943. She was commissioned on November 6, 1943. The submarine USS Picuda (SS-382) was started on the same day, in the same drydock. They were both launched on the 12th of July. Picuda was commissioned about three weeks before Pampanito. The Portsmouth Naval Shipyard commissioned 32 of these submarines in 1944 alone.
NOTE: When a submarine is commissioned, the shipyard has completed construction work. Builders’ trials and acceptance trials have been completed. The full crew is aboard and the Navy has accepted the boat. However, further sea trials may still be pending, along with the need to fix any of the issues discovered at that time. Generally, those issues are minor leaks, squeals or equipment not quite performing up to specifications. Most of these problems were resolved quickly.