As a base for the allied Mediterranean expeditionary force, and as a training ground for Australian, Indian, and British troops, Egypt in 1915 was of the utmost military importance to the British Empire. From the great camps around Cairo and the canal, forces could be dispatched for service in Europe, Mesopotamia, and at the Dardanelles, while fresh contingents of soldiers were constantly arriving to take their places. On July 5, 1915, a body of Turks and Arabs from Yemen in southwest Arabia made a threatening demonstration against Aden, the "Gibraltar of the East," on the Strait of Perim at the entrance to the Red Sea. They were equipped with some field guns and light artillery, and crossing the Aden hinterland near Lahej, forced the British to retire on Aden. On July 29, 1915, Sheikh Othman, which had been abandoned by the British on their retreat on the 5th, was again occupied by them, and the Turks and Arabs were expelled. The British troops drove the enemy for five miles across the country, causing some casualties, when the Turks and their allies scattered and disappeared. PART II--WAR IN THE AIR CHAPTER II RAIDS OF THE AIRMEN The war in the air developed into a reign of terror during the second half of the first year of the world catastrophe. While the armies on the land were locked in terrific conflict, and the navies were sweeping the seas, the huge ships of the air were hovering over cities with a desperate resolve to win on all sides. By degrees the pilots of the various nations learned to work in squadrons. The tactics of the air began to be developed and opposing aerial fleets maneuvered much as did the warships. Long raids by fifty or more machines were reported, tons of bombs being released upon cities hundreds of miles from the battle line. The German ambition to shell London was realized, and the east coast of England grew accustomed to raids. The spirit of the British never faltered. Perhaps it was best typified in the admonition of a Yarmouth minister following a disastrous Zeppelin visit, who said: "It is our privilege, we who live on the east coast, to be on the firing line, and we should steel ourselves to face the position with brave hearts." Casualties grew in all quarters. French cities were the greatest sufferers, although French airmen performed prodigies of valor in defending the capital and in attacks upon German defensive positions. But the stealthy Zeppelin took heavy toll on many occasions. It was shown that there was no really adequate defense against sudden attack from the air. Constant watchfulness and patrolling machines might be eluded at night and death rained upon the sleeping city beneath. The spring of 1915 found the air service of every army primed for a dash. The cold months were spent in repairing, reorganizing and extending aerial squadrons. Everything awaited the advent of good weather conditions.