Portsmouth Harbour repays another look. Portsmouth is on Portsea Island, connected to the mainland by a short bridge.
The western side of Portsea Island is connected to Whale Island also by a bridge though before the modern bridge there was a fordable causeway at low tide as can be seen in this postcard dated 1906.
Apparently both were used, the bridge one way and the causeway for traffic from the opposite direction.
Wiki has a map of Whale Island from 1833 which shows how it looked before the harbour was dredged
The shape is quite extraordinary to my eye, probably not natural.
The harbour was unsurprisingly heavily fortified. A tower called James Fort was built on Burrow Island at the neck of the main harbour
As per the above map of 1668 from this site http://www.fortified-places.com/gosport/
, it is clear that Burrow Island was firmly attached to the mainland. This is a more general map of the layout, dated 1678, which shows Burrow Island had the same strangely curved 'tail' (quay?) as Whale Island.
The tail shape might be why Burrow Island is also called Rat Island. A sailor's pigtail is often called a rat (and, pleasingly apt, spelt backwards it's tar!) though it may be that the island with its fort was seen as the first defence of Portsmouth's dockyards and rats famously are said to be the first to leave sinking ships.