British anti-invasion preparations of 1803–1805 were the military and civilian responses in the United Kingdom to Napoleon's planned invasion of the United Kingdom. They included mobilization of the population on a scale not previously attempted in Britain, with a combined military force of over 615,000 in December 1803. Much of the southern English coast was fortified to repel a French landing. However Napoleon never attempted his planned invasion and so the preparations were never put to the test.