The exact location of a National Projectile Factory used during World War I in Hackney Marshes was crowd sourced via Social Media. On Facebook, Diana Zanon traced the location to an area of grassland on the western bank of the River Lea in the London Borough of Hackney. The exact location of the factory was confirmed by Simon Smith on Google + who shared a photo of the factory in the 1920s from Britain from Above (http://www.britainfromabove.org.uk/image/epw005749). On Twitter Maurice Nicholson @kellsmk responded by telling us that between 1915 and 1922, 37.5 acres were taken from Hackney Marsh for the Government War Department's National Projectile Factory manufacturing munitions. Later the area was cleared to provide Mabley Green Recreation Ground, which remains a large open playing field today.