Hi Dan, Chris, Ian and Joe.
You'll have to change the color on your model. There are two ways to do it. Either overpaint the hull with dark gray, but you'll end up probablly with a thick layer of paint and probablly loose any hull detail, or remove the red paint. I have a method of doing that which is very successfull, recently I removed the paint from my type XXI Revell model. I 've built, out of wood, a "dry-dock" covering the inside with silicone to keep it dry. I am not using any kind of thinners, I am using liquid washing chlorine, used to remove difficult stains from white clothing. CAUTION: liquid chlorine is very powerfull and you should add water to it, other wise you'll end up with a melted pile off plastic. I used 750ml of liquid chlorine and added aprox. 2.5 - 3lt of water, submerged the model in that "mix" and left it there for 12 days. After 12 days the paint had peeled off completelly and if any paint was still left, it was removed VERY easy with an old teeth brush. CAUTION: chlorine fumes are hazardus, so, do it either in the basement or out-doors, anyway, don't try this in areas you and your family live in.
U-99 model is ok but you have to add a lot of work and detail on the coning tower area, plus add a few details on the deck gun and A/A gun.
If you want an acurate IXB Academy model, you have to alter the stern part and put twin screws and rudders, or the model gives the option to leave the whole underwater section out and built a waterline model.
There is another motorized u-boat model, a type VIIC, again the stern section has to be altered. It comes from a company called LEE, 1/150 scale, product Nr. 00901.
All the best to all of you,
Rgds, George Roumbos, Greece