What does that mean? How far could they operate from San Francisco?

Our submarines did not operate from the West Coast all the way to Japan or to the shipping lanes in the South China Sea. It was too far and would have taken too long just to get to the patrol area and back. In some cases, there wasn't enough fuel either. There wouldn’t have been very much time left to find and attack Japanese ships. From the approximate mileage chart, below, it would have taken 36 days just to get from San Francisco to Japan and back. It would have taken about 50 days to get to the South China Sea (using the distance to Hainan Island) and back.

Homeport for most of our boats was in Pearl Harbor, Oahu, Hawaii. That shortened the transit time significantly. By creating a refueling stop at Midway Island, the range of the boats was extended even further. Now, instead of taking 18 days to get to Japan from San Francisco or San Diego, it would only take nine from Midway. Instead of 25 days to get to the South China Sea, it would only take 16.

The numbers in the following table are rounded approximations. Some notes regarding the table:

1. San Francisco is used as an approximation for the West Coast. The distance to Hawaii from San Diego is actually a bit greater than that from San Francisco.
2. Hainan Island, China is used as an approximation for the South China Sea. The distances to the Luzon Strait and the Formosa (Taiwan) Strait, where many of our attacks were concentrated, were somewhat shorter.
3. Pampanito’s first war patrol was initially to Johnston Island to refuel and then to Yap in the Caroline Islands. Therefore, those distances are included.
4. On Pampanito’s third war patrol, she rescued 73 British and Australian soldiers from the South China Sea near Hainan Island. She then proceeded at best surface speed to Saipan in the Mariana Islands where the nearest forward base was located.
5. The number of days required was estimated using 250 nautical miles per day, traveling at about 10 or 11 knots. The journeys from Hawaii to Johnston Island or to Midway, and from Hainan to Saipan assume 400 miles per day. Those transits were at higher speed, and an average of 17 knots was used.