Nice picture; what was interesting in WWI (and to a lesser extent WWII) was Germany’s use of surface ships as “commerce raiders”. The use of U-boats came about because the Royal Navy made them fairly ineffective.
In an old Time/Life book my family had when I was younger, there was a story of one of them (the Emden?) and its struggle to get back to Germany at the onset of WWII (IIRC); when the war started they may have been near Australia.