During the Civil War, the air force became a weapon of mass destruction for the first time. Planes from fascist Italy - Franco's ally - systematically attacked Catalan cities. They bombed not just military or industrial targets, but were often indiscriminate in their choice of objectives, affecting the civilian population. The air force was a psychological weapon of the first order. Its aim was to sow terror and to demoralise the rearguard. Citizens organised their own defence, building air-raid shelters everywhere and taking all kinds of steps to minimise the effects of the bombing.