isle of grain martello tower river medway kent england uk

grain isle united kingdom martello tower mid century gun situated offshore east kent standing mouth river medway originally buily built mid-19th-century 1855 wing brick accomodation block acomodation accommodation barrack observation world war preparation anticipated napoleonic invsituated french invasionsituated invasion sheerness sheppy sheppey rocharkent rochester england thames estuaryopposite estuary