Sami marches on. Just lost again 15-16. Getting better at least.
Main thing I could come up with is shitting out infantry as soon as you get on an island and literally putting them all along the coast so no enemy landers can dock.
It normally takes at least 5 or 6 turns before Sonja starts landing troops on the north island. By then, you should already have control of the island and started capturing properties. You should use your sub and cruiser as spotters and your battleship as covering fire for landing a tank and an infantry-loaded APC onto it. Then you can keep sending your remaining infantry there while your vehicles land on the south island (after already landing two footsoldiers to capture the properties there) to keep Sonja's forces occupied. By the time Sonja's landing troops, you should've already crippled or destroyed the opposing battleship with your sub.