May 17, 1915, was a bad day for Zeppelins. One of the dirigibles supposed to have attacked Ramsgate early that morning was discovered off Nieuport, Belgium, by a squadron of eight British naval machines which had made a sortie from Dunkirk. They surrounded the enemy craft and three of the pilots succeeded in approaching close to the Zeppelin. Four bombs were dropped upon the airship from a height of 200 feet. A column of smoke arose. The Zeppelin looked as though it would fall for a moment, but righted itself and mounted to an altitude of some 11,000 feet, finally eluding its pursuers. Two Zeppelins and two Taubes were caught by daylight after a frustrated raid upon Calais on May 18, 1915. They were fired upon from many points. A battery at Gris Nez succeeded in hitting one of the dirigibles. The other craft of the flotilla stood by their injured fellow as long as they dared, but made off after a few minutes, as French machines were closing in from all sides. The injured Zeppelin dropped on the beach near Fort Mardick, about two miles from Dunkirk. Forty men aboard were taken prisoners, including several officers. Two women in Southend, England, met death on May 27, 1915, when Zeppelins visited that city. A child was badly injured. The lighting plant and several industrial establishments suffered damage. Repeated attacks on Southend had resulted in the installation of searchlights and the detailing of more aviators to guard its citizens. Neither availed to prevent the loss of life, but they did succeed in driving away the raiders after their first appearance. Of all the raids carried out during the spring and summer of 1915, one of the most important was that upon Ludwigshafen, in Bavaria. Here the laboratories of the Badische Anilin und Soda Fabrik were located. This plant was said to produce two-thirds of the nitrates used in the production of ammunition for the German armies. Since the start of the war it had been the object of several attacks, none of which had noteworthy results.