In 1940 General William Ironside, Chief of the Imperial General Staff proposed plans to defend and fortify the country to counter the threat of German invasion. Ironside pronounced his plan would - "Prevent the enemy from running riot and tearing the guts out of the Country."
Troops constructing Z1 invasion barrier
Lieutenant-General Thorne was appointed to oversee the defence of Kent and the South East of England and Kent. Thorne considered the enemy would make landings between Graveney and Dover and he ordered the construction of obstacles and fortifications laid down a line across the marshes incorporating the railway and where possible natural features. The defences became known as the – ‘Coastal Crust’.