That tanker carried one-third of the oil available to the Wehrmacht in 1940! Even the Nazi leadership realized a cross-channel operation had become impossible, and accelerated their plans to invade the USSR -- which included capturing the oil fields to the south.
They did get their revenge in the end. Once they found the USS Sea Lion was responsible, they informed their Italian and Japanese allies. The IJN took it very seriously. They did what they could to track the American sub, in the period leading up to Pearl Harbor, and, somehow -- despite unreliable intel -- they succeeded in destroying it.

In memory of USS Sea Lion
