The original upper wing and fuselage markings for 1937 camouflaged RAF aircraft were roundels of (from center) red-white-blue-yellow. Squadron was shown by colored numerals with the unit number on fin or fuselage. Both items were pretty visible, so in August-September of 1938, teh roundels were changed by overpainting the yellow in the appropriate camouflage color (Dark Earth or Dark Green, and covering the white ring by extending the blue and red portion to meet each other. The squadron numbers were overpainted and replaced by two-letter codes in Medium Sea Grey denoting the squadron on one side of the fuselage roundel, and an individual aircraft letter on the other side. These squadron codes were actually 'pre-wartime' codes; when when war broke out in September 1939 they were to be changed to a different predetermined set of letters. Needless to say, in 1938 a couple of squadrons used the letters from the wrong list and had to have their codes changed to the correct 'pre-wartime' combination,