Longest Runway in Iceland?

Many years ago we used to get regular issues of the En Route Docs, etc, from Northolt.
I seem to remember that in one of the very early ones (early 50's) there was an airfield in Iceland which had 3 parallel runways. Each was 17500 feet long, and larger than standard width. The theory was, that when they were flying relatively short range fighters/fighter-bombers from N America to Europe during WW2, they could put 9 a/c on this concrete (3 - lengthwise spaced - on each runway, and 3 runways) and thus get them to take off simultaneously! Must have been quite a sight!!
Was this actually so? And if, where was it? Can't see many soil/crop marks near Keflavik to account for this!
Or am I dreaming this?
HTH
Resmoroh