What is militarily and engineeringly possible may :-

Be Political unfeasable,

Of no practicle use.

Doug R - You still have not answered the point on the Maginot Line - which was "high tec" at the time it was built. Or what happened to the Dutch and Belgium equivalents.

A standard 40 foot ISO shipping container has a pay load of 30 long tons.

Can a mercantile nation such as the USA quarantine (well off shore) and search every container ?

Gareth