Grange Redoubt was built in 1885 and Woodlands Redoubt in 1888.
Both were built in lower Gillingham to defend Chatham Dockyard and military establishments from a landward attack via the Gillingham side.
They were not included in the original proposals of the 1960 Royal Commision but were later additions.
The Redoubts are similar in design and were built as experimental semi-permanent field fortifications.
In the event of an attack to be supported by Batteries from the rear of the Redoubts.
The design of the Redoubts was a D shape with shelter provided by concrete casemates reinforced with rail track and earthed over.
Unlike the Chatham and Rochester forts,the ditch in front of the parapet dropped away at a steady angle of 1 in 6 that sloped down till it reached about 10 feet below ground height.
At the bottom was a Steel unclimable Palisade.
Also barbed wire,felled trees and mines could of been used as obstacles.
On the Counterscarp side of the ditch was a 10 feet sheer wall up to ground level.
This type of revetment became known as "The Twydall Profile" and was used for a number of years at defensive sites in Britain and overseas.
The idea of this design was so that the Redoubt blended into the surrounding countryside.
The Redoubts were built by contractors under controlled conditions to a fixed price contract and to be completed by 30 days to simulate war and invasion conditions,using only locally available materials and manpower.
No machinery could be used either.
When finished the Redoubts would have a garrison of about 200 men who would be billeted in a camp well to the rear and only man the Redoubt in time of invasion.
Woodlands Redoubt had a length of 220 feet from ditch edge to ditch edge and 110 feet wide at the cetral point.
Today the Woodlands Redoubt has still got it's Casemates,entrance and earthworks to the rear,but the front earthworks have gone.
The site has been used as a cold store and later as a factory unit.
Grange Redoubt has no Casemates left but the front earthworks are nearly complete and even some sections of the Palisade remain.
Both sites are on private land and used as stables with no public access possible.
The future of the sites is uncertain and even open to re-development or demolition.