Grain Fort was one of a number of forts built to defend the Thames Estuary. It was built between 1861 and 1868 and consisted of a polygonal earthwork around a central semi-circular keep. There was an outer ditch with four caponiers and a second inner ditch between the earthwork and the keep defended by a further five caponiers. The main magazine was located beneath the keep with tunnels linking to the caponiers and the ammunition lift to the gun emplacements above.
The fort remained operational throughout WW1 and WW2 and was finally abandoned in 1956. The keep and all other surface buildings were demolished during the 1960’s and the whole area was in-filled with soil and rubble as were the emplacements on the terreplein. Apart from the earthwork itself there is now little evidence of the fort to the untrained eye other than two brick retaining walls at either end of the earth work and remnants of the in-filled emplacements. The network of underground tunnels and magazines must, however, remain intact beneath the ground.
When inspected in 1998, the truncated end of one of the outer caponiers was visible in the ditch and a small hole in the concrete proved beyond doubt that at least one tunnel still existed although the size of the hole, a mere 3 inches across, left little scope for further exploration.
Since that date the hole has got progressively larger, no doubt the children from the local council estate have spent many hours chipping away at the concrete and when inspected again in June 1999 it was found to be man sized. On the 11th of June 1999 a party from Subterranea Britannica, Kent Underground Research Group and the Kent Defence Research Group entered the tunnels.
The hole was in the top of the wall sealing the butchered end of Caponier No. 2 (As labeled by RCHME [now part of English Heritage] in their 1998 survey of the fort). The passage entered was of brick arched construction and painted white. After a few yards the demolished section of the caponier has been backfilled into the passage but it is possible to clamber over the large blocks of rubble and past 24 metres there is a pit in the floor, 1.8 metres deep. It is dry and contains a little rubble and is bridged by a sturdy wooden plank. This was the site of a chicane or small drawbridge, a remnant of the wooden decking still remains in place and the pivot and counter balances are inset into either wall and are not accessible. Examples can still be seen in the Detached Bastion at Western Heights in Dover and at Fort Purbrook. There is a metal grill in the arching above the chicane. At this point the passage narrows from 2.5 metres to 1.5 meters, turning to the north west and sloping gently upwards.
After 19 metres a junction in reached. Turning left there is a doorway on the left after 10 metres leading into what is described in an 1895 plan of the underground elements of the fort as a ‘shell store’, but the shape and size of the room doesn’t match the plan so this store may have been at another level. This is a small room measuring 3 metres by 3 metres. There is a hand cranked cartridge lift for the 10 inch H.P.B.L. (installed around 1895) still in situ but the shaft is capped about 20 feet above. The room has three small recesses in the wall. The remains of three metal beds are leaning against the wall.
Diagonally opposite the entrance to this room is the issue hatch from the main magazine with the wording ‘issuing hatch’ still discernible on the wooden surround. The hatch itself is missing and is to be found leaning against a wall in one of the other tunnels. The main passage now turns sharply to the right where there is another junction. To the right a doorway leads into a small shifting lobby with a lighting recess high in the wall lighting both the shifting lobby and the magazine. There is evidence of wooden shelving on the walls and a second doorway that leads into the main magazine. The remains of the two wooden doors lie on the floor in the shifting lobby with some lettering just discernible. The magazine is of cavity wall construction and there are a number of openings into the cavities with a wooden framework that originally supported long thin wooden doors. The magazine measures 6 metres by 12 metres with an arched roof approximately 3 metres high in the centre. There is a second lighting recess at the far end; both recesses have a copper lined conical flue. There is a wood lined sloping shaft approximately .25 metre square in the ceiling with a pile of fine soil on the floor beneath it.
Returning through the shifting lobby there is a wider (2.5 metre) passage that is almost blocked with a large amount of material that has come through an opening in the roof presumably made when the buildings above were demolished. It is possible to squeeze through the infill that hides another lighting recess on the right hand side. After a few feet a narrow lighting passage comes in from the right and the main passages continues to a ‘T’ junction after 15 metres. At the ‘T’ junction there are small arms left and right with blocked loopholes for defending the inner ditch, each running for 7 metres with a wall half way along. At this point was one of five caponiers across the inner ditch but the entrance has been very neatly walled across, probably long before the demolition of the keep above. From the infill to the end of the passage, including both arms of the ‘T’ the floor is strewn with rubble. All other passages are clean and free of rubble and surprisingly also free of graffiti - but for how long?
The lighting passage turns through a ‘Z’ bend, where there is an open drain in the middle of the passage which widens out to 1.5 metres as it runs along the west wall of the main magazine. There are steps up to the lighting recess for the shifting lobby/magazine. After 18 metres this passage comes to a ‘T’ junction, right leading back to Caponier No 2 and left sloping downwards to a second chicane position. The pit is partially water filled and is bridged by an unsafe wooden plank. Again a remnant of the decking and the pivot and counter balance remain in situ. The passage widens to 2.5 metres after the drawbridge and is blocked by infill after 10 metres. There is evidence of electric lighting (metal conduit and fittings) throughout the tunnel system.
In their recent report on fortifications at Grain the RCHME highlights the potential hazards should local children get into the tunnels. It would appear from their report that they did not enter the tunnels, presumably because the hole was too small at the time. Although this section of the tunnels is not extensive and does not give access to the rest of the network, the two chicane pits and the open drain could certainly present a hazard to local children exploring without adequate lighting although the structure of the tunnels themselves is sound and there is little danger of anything collapsing.
On a subsequent visit for surveying and photography a bat was seen on the wing so it would be illegal to seal the hole permanently. On first examination the smooth tunnel walls seemed an unsuitable roost for bats but the wall cavities might prove more suitable, so a secure lockable grille on the gaping hole would seem a sensible precaution especially because of the close proximity of a large housing estate.