<P> Consolidating merchant ships into convoys protected by one or more armed navy vessels was adopted later in the war . There was initially a great deal of debate about this approach, out of fear that it would provide German U-boats with a wealth of convenient targets . Thanks to the development of active and passive sonar devices, coupled with increasingly deadly anti-submarine weapons, the convoy system reduced British losses to U-boats to a small fraction of their former level . Lieutenant Otto Weddigen remarked of the second submarine attack of the Great War: </P> <Table> <Tr> <Td> "</Td> <Td> How much they feared our submarines and how wide was the agitation caused by good little U-9 is shown by the English reports that a whole flotilla of German submarines had attacked the cruisers and that this flotilla had approached under cover of the flag of Holland . These reports were absolutely untrue . U-9 was the only submarine on deck, and she flew the flag she still flies--the German naval ensign . </Td> <Td>" </Td> </Tr> </Table> <Tr> <Td> "</Td> <Td> How much they feared our submarines and how wide was the agitation caused by good little U-9 is shown by the English reports that a whole flotilla of German submarines had attacked the cruisers and that this flotilla had approached under cover of the flag of Holland . These reports were absolutely untrue . U-9 was the only submarine on deck, and she flew the flag she still flies--the German naval ensign . </Td> <Td>" </Td> </Tr> <P> Between late 1914 and early 1918, the Western Front hardly moved . The beginning of the end for Germany was a huge German advance . In 1917, when Russia surrendered after the October Revolution, Germany was able to move many troops to the Western Front . Using new stormtrooper tactics developed by Oskar von Hutier, the Germans pushed forward some tens of kilometers from March to July 1918 . These offensives showed that machine guns, barbed wire and trenches were not the only obstacles to mobile warfare . </P>

Which of the following military tactics was used for the first time in world war i