How long were war patrols?

These WW2 boats were designed for war patrols of up to 75 days. A few patrols even went a bit longer. However, from what we can tell from the histories, most patrols were between 45 and 60 days each. If fuel was used quickly, because of the need to run at higher but less efficient speeds, the patrol could be shorter. If you used all your torpedoes or suffered significant damage, you would also return to port sooner.

Returning to port early because you used up your torpedoes didn’t always get you all of the usual break. There were instances where skippers found abundant targets and fired all their torpedoes fairly quickly. Occasionally, when those skippers returned to a base, they opted to just reload torpedoes, top off food, fuel and other supplies, and head back out quickly to finish the patrol.

War patrols did appear to get shorter as the war progressed and we pushed the Japanese back to the west. We established advance bases as we defeated the Japanese. After the Battle of Midway, we could have been confident enough to do maintenance and resupply at that island rather than just refueling. After defeating the Japanese in the Marianas, we established bases at Saipan and Guam even while some Japanese soldiers were still fighting on those islands. The same was true of the Philippines. Again, there was still fighting in the islands when the tender (support ship) was established in Subic Bay. With the reduction in transit time to the combat zones, and with more and more submarines in commission, the patrols could have been shorter.

Generally, Pampanito’s war patrols ranged from 42 to 59 days. However, her fifth patrol was only a bit over two weeks. (Sources differ on the exact length.) She was almost out of torpedoes and had a very short transit to her next port, Subic Bay in the Philippines.