HIP-S-000267-2768 Air raid warning device, World War I, 1918. Copy of two photographs showing a sound detector. During the First World War acoustic detection devices were used to warn of enemy aircraft. The photographs were taken for the Ministry of Munitions Credit: Historic England Archive / Heritage Images /Alinari Archives, Florence WARNING: Permission must be required for non editorial use. Please contact Alinari Archives Date of photography: 1918 Collection: Heritage Images /Alinari Archives, Florence Object type: digital image Photographic technique: P digital image Technical info Image sizes (pixel): 4929 X 3510 Image sizes (cm at 300 dpi): 41 X 29 Image sizes (MB): 4.33 Color space: RGB