 Complete the following phrase:  Preussischer Adler was sent to the Mediterranean Sea in September 1863 in company with a pair of gunboats, but shortly after they arrived, they were recalled owing to an increase in tension between Prussia and Denmark that resulted in the Second Schleswig War. While on the way back to Prussia, the three ships rendezvoused with a pair of steam frigates from Prussias ally Austria. The combined squadron attacked a Danish force enforcing a blockade of the German North Sea ports, resulting in the 