£1.50 No.4450 Fokker D XXIII Normally if you put twin engines on an aircraft, you increase the drag so much that you don’t get the full benefit of the extra power. Unless, of course, you stick one behind the other. It’s a clever idea but can, as the designers of this Fokker found out, lead to cooling problems for the rear engine. They didn’t get time to sort those out, either, for the German invasion of theNetherlandsbroughtworktoahalt.