Invasion!
"If, in 1939 or early 1940, an invading fleet had breached air and naval defences, they would have found much of Britain's coastline poorly protected. Coastal batteries were located at Landguard Fort [Felixstowe] and Lowestoft but, at the outbreak of war, much of Suffolk's coast was defenceless". (From Suffolk's Defended Shore by Cain Hegarty and Sarah Newsome, English Heritage 2007 p.53)

