Torpedoes, submarines, and the German response

Would larger ships drive bigger torpedoes and submarines, or earlier explosive improvements?

Possibly, but it depends on whether Germany tries to match the cruiser force or shifts resources earlier toward submarines as its battle fleet loses relevance.

The German response remains an open design-and-production question. Larger targets might encourage bigger torpedoes or earlier work on more powerful explosives, but those programmes still compete for finite resources. If Germany tries to match the new surface ships, the extra construction burden could constrain torpedo development. If its battle fleet becomes less relevant sooner, submarines may become more attractive earlier in the war.