Trains and supply trucks on the move as well as barges at the ports are targets in the supply chain.
At bases there are ammo bunkers, troop barracks, fuel tanks, fighter hangers, vehicles hangers, bomber hangers, radar tower, field guns both manned and auto. There are also non-strat structures that can be destroyed.
Towns, all the buildings can be destroyed as well as ack guns there too.
There are strat areas that are used in the supply system in the game (trains, convoys both ship and trucks come from) where all building, towers and guns can be destroyed.
There are fleets at sea and all ships in the fleet can be destroyed.
There are plenty of targets for the bomber guys.