Main difference between type VII and IX is that the type IX is longrange uboat that
operated near US coast, Caribbean and the far east. It could carry more torpedoes that the type VII, but it had longer dive times and was larger.
That would proove as disadvantage, because if the boat is suprised by aircraft it
just couldn't dive fast enough to avoid being damaged.
Also, because of it's size, it's easier to track her with sonar, and hit her with depth charges or hedgehogs.
