Military naval vessels record the weather six times a day. Because ships move around, we can think of them as de facto mobile weather stations. Britain’s National Archives has scanned the logs of 250 ships from the extended First World War period, from 1913 to 1923. Old Weather asks us to help transcribe these 250,000 log pages. What we find there will help scientists to understand what the weather was like 100 years ago. This reconstructed weather information may give us insight into climate change today.