I like your original idea, but what about carriers? They were the most important ships to keep afloat during the war, and a great deal of repair was done for them as well.
I do not recall any instance off-hand during the war in which a carrier was re-floated after having been sunk and then returned to active service.
The Amagi and Graf Zeppelin were both sunk and re-floated, but neither saw active service during the war and Graf Zeppelin wasn’t even complete.
The re-floating idea is kind of cool, but it may need to be reduced somehow to make it a more rare occurrence. As Marc said, it was a long and expensive process and not every ship that was sunk qualified for such a salvage operation. Unfortunately with A&A, we do not have the granularity in gameplay to determine how badly ships are damaged.
I suppose that you could modify the rule so that after combat you need to roll for each ship lost to determine IF it can be salvaged. Say you need a 2 or less to float a given ship. If you roll that, then you can decide to pay half to re-float.
It complicates things, but definitely makes it so you can’t just regenerate 2 battleships and 3 cruisers if you want.
I will offer another limitation that sounds logical to me, but you can consider:Ships may only be raised on the following turn and to do so, there may not be any hostile warships in the sea zone where the ships were sunk. This implies that any ships not raised the following turn will be lost forever, as you said, and that the territory with your naval base cannot be taken by the enemy in that time.
Example: Gibraltar is amphib assaulted by Italy. All UK warships are destroyed. Italy has no warships present in sea zone, only transports. Italy takes Gibraltar. US player lands and liberates Gibraltar on their turn, returning it to UK control. The UK player cannot then re-float ships lost in previous turn combat with Italy because they did not retain full control of Gibraltar.
Somewhat complicated perhaps, but I think some of these limitations need to be placed, otherwise I see this as being a huge advantage for the Axis. Germany and Italy in particular, because they tend to hole up their navies in home water areas and can potentially get double the naval power at half the cost. It will further incentivize them to stock up and stay in port knowing they can effectively respawn capital ships on the cheap. An element of chance and tactical consideration should be added so that it isn’t just automatic.