Charles I have been interested in the Lw and German navy involvement for decades. It was not at all good during the war but in this case it worked in unison.
check this thread I started and hopeful it will help some
Wonderful pictures - also if you visit Wikipaedia - and look for DO214 or Do216 you will see a splendid model of the the gigantic sea plane intended for military service by the Luftwaffe which was never built ... makes the BV238 look small .
Try also DO24
Italy also had an interesting range of Sea plane /Float plane variants