A British squadron bombarded the German fortifications on the Belgian coast, from Zeebrugge to Ostend, for two hours on November 30, 1915. The weather suddenly changed on the entire western front. Rain, mist, and thaw imposed a check on the operations, which simmered down to artillery bombardments at isolated points. For the next three months the combatants settled down to the exciting monotony of a winter campaign, making themselves as comfortable as possible, strengthening their positions, keeping a sharp eye on the enemy opposite, and generally preparing for the spring drive. Great offensive and concerted movements can only be carried out after long and deliberate preparations. The Allies had shot their bolt, with only partial success, and considerable time would have to elapse before another advance on a big scale could be undertaken. Hence the winter campaign developed into a series of desultory skirmishes and battles, as either side found an opportunity to inflict some local damage on the other. For the Allies it was part of the "war of attrition," or General Joffre's "nibbling process." The Germans had gone through a bitter experience in Champagne; with characteristic skill and energy they set to work improving their defenses. At intervals of approximately 500 yards behind their second line they constructed underground strongholds known as "starfish defenses," which cannot be detected from the surface: About thirty feet below the ground is a dugout of generous dimensions, in which are stored machine guns, rifles, and other weapons. Leading from this underground chamber to the surface are five or six tunnels, jutting out in different directions, so that their outlets form half a dozen points in a circle with a diameter of perhaps 100 yards. In each of the tunnels was laid a narrow-gauge railway to allow the machine guns to be speedily brought to the surface. At the mouth of the tunnels were two gun platforms on either side, and the mouth itself was concealed by being covered over with earth or grass. The defenses were also mined, and the mines could be exploded from any one of the various outlets. On several occasions when the French endeavored to press home their advantage they found themselves enfiladed by machine guns raised to the surface by troops who had taken up their places in the underground strongholds at the first menace to the second line. When one of the outlets was captured, machine guns would appear at another; while, if the French troops attempted to rush the stronghold, the Germans took refuge in the other passages, and met them as they appeared.