For my U-Boat I airbrushed the entire model with Tamiya German Grey, I then masked off the underside waterline as you see in pictures. I then airbrushed the sides and conning tower with Tamiya IJN Grey leaving the riveted sections German Grey, I then highlighted the IJN Grey with Light Grey. I then used Rustall Black Wash and Rust on the model follwed by a very light drybrush of the U-Boat with a mixture of 75% Light Grey and 25% Flat White. Hope that Helps.