When making an amphibious assault (without naval combat), Battleships can conduct Shore Bombardment. (rulebook pages 15 & 29)
On both these pages, the rules specify that ‘…battleship fires once (…) against enemy land units…’

Does this mean that airplanes cannot be hit by Shore Bombardment?
(a critical question if all defending units are airplanes)

Nota: airplanes are NOT land units (see page 24), even while grounded.

Please make sure your responses conform with A&A 2004 Revised edition.