This proud territorial integrity has rung true in the minds of the British for almost a thousand years but the minds of military planners have always had the niggling doubt of 'what if?' to contend with. Should a force have made it ashore in 1812 or 1940, how prepared would we have been to wage warfare on home soil? That searching question led to the construction in the 1890s of the London Mobilisation Centres - a ring of fortified positions around London itself to provide land defences against any invasion force. As both defensible barracks and munitions stores, they were designed to present offensive forces with immovable obstacles, slowing any attackers down and preventing rapid advances to the capital.
Of course, history shows us that the forts never saw service. Neither of the World Wars saw our island home under serious threat of invasion and as the lack of threat receded, so the forts fell into disuse. Many of them still stand today as a reminder of a time when it did seem a possibility that Britain could be invaded from without rather than within.