Another one of my periodic musings... does it make sense that a stack doing an amphibious landing must win or die (i.e. no retreating)? Why not just retreat back to the transports you came from? I think we all kind of suffer from the "Saving Private Ryan" syndrome that leaves us thinking that in an amphibious assault one either wins or dies on the beach. I'm not sure it really applies to 19th century warfare. (And if you think of the 20th century, it's a bit over simplified. The Gallipoli force was able to evacuate from the beachhead with minimal losses, and even in the Utah Beach case a failed landing would have been called off long before the whole RCT or Division would have been committed.)
In the Civil War, I can't think of an example where a landing force hit a defended beach and was forced to surrender because it couldn't withdraw to its transports. Sherman at Chickasaw Bayou is a nice example of a failed landing in the Civil War. He lands (unopposed), moves to assault the Pemberton's defenses, is repulsed, loads on his transports and leaves. It's not like the blue bellies ate caster as they were leaping off the boats and Sherman and his command were forced to surrender on the beach.
So wouldn't it make more sense to allow a stack to retreat back to its transports following a failed landing rather than making it fight to the end? (I am not saying that anything should do with the combat penalty associated with landings...that seems rather justified.)