From that photo I think that it is not located there any more, but has been towed to a field at the northern edge of the site.
Interesting to hear that they had railway carriages there, because it was served by the Chattenden and Upnor Light Railway, apparently some of the rolling stock is now used on the Sittingbourne and Kemsley Preserved Railway.
On the same drive we saw and photographed the WW1 German U-Boat at Humble Bee Creek.