By the beginning of 1915 the horrific killing power of machine guns and artillery had taught all sides that the only way to survive was to find shelter and dig in. Nowhere was this illustrated more dramatically than at the Battle of Neuve Chapelle in March 1915, where a handful of German soldiers with machine guns held off a British force of 9,000 men. Eventually 25,000 miles of trenches would cut across Europe.With conventional weapons unable to provide a breakthrough, new technologies took the war into the sky and under the sea. Britain started the war with just 193 planes, but by the end British factories were producing over 30,000 new aircraft a year.Germany responded to the British naval blockade by unleashing their U-boats on allied shipping, but the sinking of the liner Lusitania with the loss of 1197 lives, 128 of them Americans, came close to bringing the US into the war.