The squares are flood valves, and there aren't many clear period pix. be careful of U 995 as a source, she served as a reral sub after the war and then a museum, she has been modified and is not Period Correct (torpedo shutters welded shut, many weld repairs, closed in bits and others opened up. I would levae the Revell features. Eduard and other aftermakert PhotoEtch makers have brass bits for these holes.