The Clyde has been strategically important for centuries, as we cans see from the rich landscape of prehistoric and Roman forts, medieval castles and country estates. We less often think of the Clyde as a place of power in the 20th century. Yet this was a period that saw the building of extensive military defences along the Firth of Clyde, to protect the major manufacturing and population centres along the river during the First and Second World Wars. Along with the Glasgow University’s Centre for Battlefield Archaeology and local heritage groups, we are recording and researching the defences that were built to protect from attack from the sea. These sites are almost undocumented: no excavation has ever been undertaken; most have no site record, or at best a very basic one; and none of the structures are listed or scheduled. Our investigations will help local people have a better understanding of the importance of the sites, which we hope will lead to better-informed decision-making about their future.