 Allied forces mainly limited themselves to blockading the Central Powers' navies in the Adriatic, which was successful in regards to surface units, but failed for the U-boats, which found safe harbours and easy passage into and out of the area for the whole of the war.Considered a relatively secondary part of the naval warfare of World War I, it nonetheless tied down significant forces.The Adriatic campaign was also important because for the first time two new weapons were used successfully in warfare, viz.