Lynette Iezzoni, writes in her book Influenza 1918, (New York: TV Books, L.L.C., 1999), 35, 36:

The earliest reports of epidemic influenza had come in mid April 1918, among the American Expeditionary Force disembarking at the French port of Bordeaux. By May, Americans were down with "three day fever," the French suffering from "la grippe," the Germans, "Flanders Fever" or "Blitzkatarrh," and the Italians, "sandfly fever." In Spain, eight million people were ill, including one third of all the residents of Madrid. Spain's King Alfonso XIII fell sick. So did Britain's King George V. In Berlin, Kaiser Wilhelm and 160,000 fellow Berliners were ill. All across Europe, trams stopped running and businesses and government offices closed. Influenza began affecting the schedules of war.

For twelve days in May, the British Grand Fleet remained docked; 10,313 British sailors were sick. During three days in June, P.U.O. (Pyrexia of Unknown Origin) sent three thousand British soldiers to hospital in Etaples, France; at British G.H.Q., seven hundred were sick. On the other side of the Hindenburg Line, Germans were failing at their posts as well. Some flu?ravaged divisions were down to fifty men. The commander of the German forces, General Erich von Ludendorff, complained: "It was a grievous business, having to listen every morning to the Chiefs of Staff's recital of the number of influenza cases, and their complaints about the weakness of their troops." Ludendorff later blamed the failure of Germany's July offense (which nearly resulted in German victory) on the reduced strength and morale of his troops, due, in part, to influenza.

The pain began behind the eyes, spread to the ears, the neck, the spine, and the legs. A soaring fever, chills, and delirium made for a painful, mind?numbing ordeal. In some cases, after three or four miserable days the malady began to subside. But other patients developed massive pneumonia and death came swiftly. "Purulent bronchitis"? "Flanders Fieber"? The grippe?

By now, most Europeans were calling the illness Spanish flu.

In a dilapidated Army Hospital in Cittadella, Italy, Second Lieutenant Giuseppe Agostoni huddled over a dying soldier. A twenty-five-year-old medic, Agostoni had watched in horror as influenza ravaged his regiment. But what kind of flu was this? Men were choking to death, gagging on the bloody regurgitation of their fluid-filled lungs. Faces turned grey, purple, then brown. Labored breathing produced a weird, duck-like quack.