Arms and Armour
A hardened aircraft shelter (HAS) or protective aircraft shelter (PAS) is a reinforced hangar to house and protect military aircraft from enemy attack. Cost considerations and building practicalities limit their use to fighter size aircraft.
Boom (navigational barrier).
Battle of Lincoln (1217).
Text from Wikipedia; plate via Wikimedia Commons. Text CC BY-SA 4.0; plate freely licensed (see Commons). Source record. Images and catalogue data are reproduced from open-access collections.