The reach and supply problem of a German base in Iceland

How serious a threat would a German base in Iceland have posed?

It could have threatened much of the Atlantic, but Germany would have needed a vulnerable convoy route from Norway that Royal Navy submarines could attack.

A German base in Iceland could extend German reach across a large part of the Atlantic and create a serious problem for Britain. The base would remain useful only if Germany could keep it supplied. Convoys running between Norway and Iceland would create a long, recurring route for Royal Navy submarines to attack. Capturing Iceland would still leave Germany with the recurring problem of sustaining the base.