Cut and paste follows 'cos it's sort of bits out of the middle of several pages of stuff: -

"The Medway Forts
Following a Dutch raid in 1667, a ring of forts was built around the town to protect the naval dockyard and these were improved and added to during the Napoleonic Wars. Despite the enormous cost, they never saw a shot fired in anger and Chatham today is still dominated by the largest, called Fort Amherst. Of the others, several have been demolished but some still remain, albeit hidden amongst trees or houses. These forts were smaller versions of the Dover fortifications and, although they had underground features, the local rumours of linking tunnels are not true. Fort Bridgewood, Fort Clarence, Fort Delce, Fort Pitt and Fort Darland have been demolished although a few features may still be found. Fort Borstal, Fort Horsted, Fort Luton, Twydall Redoubt and Grange Redoubt still remain at the time of writing but permission must be obtained from the respective landowners before visits. The most impressive was Fort Amherst and, luckily for posterity, this has been preserved. It is open to the public and volunteers often dress up in period military uniform.

World War I
This marked a change in the pattern of warfare since the fighting took place in the trenches of France and Belgium, with no requirement for new fortifications in Britain. It did bring in a new development, however, whereby men of the Royal Engineers began to tunnel under the enemy trenches to lay explosive charges, hence the derivation of the word 'mine'. The base depot of the Royal Engineers was at Chatham and the area was used to experiment with new techniques of mining, since the local sand and chalk was almost identical to conditions at the Front. Very few of these trial mines were recorded at the time and, although it is likely that many collapsed subsequently, some still turn up in surprising places. The latest example was discovered following a collapse in a Gillingham back garden in 1988.

During the construction of a roundabout at the junction of the A2 and A278 in Gillingham, a set of 6 galleries was found which had been unsuspected. They were found to be on three levels from 20-50ft below the surface, being dug as a model for mining operations under Hill 60 in France and the subsequent battle at Messines. Each gallery consisted of an entrance tunnel which led to six chambers, each 20ft wide x 30ft long x 7ft high. They were in a very dilapidated condition and had to be completely infilled.

World War II and After
.......... It is highly likely that other undisclosed military installations exist in Kent and Sussex that are still regarded as military secrets.



Ramsgate Air Raid Tunnels

............

Rochester Civilians also needed air raid shelters and large communal ones were made by adapting existing tunnel systems at Chatham, Rochester, Sevenoaks and Chislehurst.
.....