I used to go camping on the barrier isles on the Mississippi Gulf Coast. It's beautiful out there, but Hurricane Katrina literally redrew the map.

The British are fond of using this term (Isle of Man, Isle of Wight, etc.), but there is no clear distinction between an isle and an island.  

In Middle English there was no s and the word was either spelled ile or yle.  The word, however, is probably derived from the Latin word insula (island).  Possibly also borrowed from the Old French, ille. 

58 minutes ago, Bill W said:

Is that semi-circular structure a fort?   And if so, was it constructed for the Revolutionary War or the Civil War? 

That is, believe it or not, Fort Massachusetts. Fort Massachusetts was built after the War of 1812 by the fledgling US War Department to protect shipping routes.

It was abandoned by the Confederates early in the Civil War, as it was impossible to resupply in the face of Union Naval supremacy. It was occupied by Federal forces and used as a staging base for operations.

The National Park service owns it now and tour boats out of Biloxi bring out  tourists daily depending on the season and weather.