Welcome to the forum, chaikov.
You read it correctly, in Revised OOB only land units can be hit by Shore Bombardment, that excludes airplanes.
Air units can be additionally hit starting from the Revised LHTR ruleset and in later games.
Let’s say I have a transport with 1 INF and 1 ART attacking enemy territory. In Round 1 I score 1 hit and the defender scores 1 hit. Can I take the TRN as the casualty so my 1 INF and 1 ART can fight in Round 2?
No the Tranny doesnÂ´t participate in the land-battle and canÂ´t be taken as casualty.
It does participate in the naval battle before the amphibious assault (if there is one) and could be taken as casualty there, but all units it has loaded would be destroyed.