I agree with knp77, Liners should take infantry only. Too much trouble to carry a Tank down the stairs.
I read about this topic some years ago. An infantry division would need more space than an armored division. An inf div have more men. Also, the 1000 horses and tons of hay of an infantry div take lots of more space than the 200 trucks and fuel of an armored div. And that is the reason for that USA in the real war sent so many motorized and mechanized divisions to Europe, they took less space on the trannies. And in the Pacific, the Marine units did not need horses, they got supply directly from the ships.
I read on the Designers forum some years ago, the reason a tranny take one inf and one other land unit, is the designer was afraid that the USA player would stop buying infantry if a tranny could take two Tanks. So, the rational was playability, not historical facts.
About the doubblehits. Bismarck took 800 hits from guns and torpedos and still did not sink, the crew had to open the bottom valves. Tirpitz got bombed and torpedoed many times, and after the last bombing she was so damaged they cut her up for scrap metal, but she never sank. This are the true battleships. As mentioned above, Lusitiana sank by one torpedo, and even Titanic sank by one iceberg. Liners are not unsinkable.
I think that some nations should start with a few liners, since they in fact were confiscated at the beginning of the war. No liners was build during the war.
USA, UK and Ge start with liners. Move 2, carry 3 units, infantry only, debark into friendly territory and during non-combat move only, sink by one hit