In October 1918, an Allied army (Egyptian Expeditionary Force) in Palestine experienced simultaneous epidemics of falciparum malaria and influenza during the cavalry campaign that defeated the Turkish Army. Malaria infection occurred 2 weeks after the advance of cavalry units into areas without environmental mosquito control. Pandemic influenza, now thought to be an A/H1N1 strain, struck at the same time. In the Egyptian Expeditionary Force of 315,000 soldiers, 773 died from malaria and 934 from influenza-pneumonia. Disease casualties outnumbered those due to combat by more than 37 to 1. Simultaneous infectious disease epidemics can cause mass casualties, capable of overwhelming any health service.