One more point to add to what Bruv119 and Virage said. The town has one building you cannot destroy. It is the large hanger like building. So every building except this needs destroying. (Including radio masts, water towers).
Buildings can be destroyed by almost any means, bombs, rockets, machine gun bullets, shells from ships or vehicles. However whilst one bomb may knock out a building (or two) it would take a heck of a lot of bullets to do the same job.
If you drive a tank to a town, you want HE rounds (High Explosive) as fewer are required than AP rounds (Armour Piercing). Ideally take mostly HE rounds with a few AP to defend against the enemy tanks if they should show up! It typically takes two HE rounds to knock out an undamaged building. Perhaps twice as many if using AP rounds.
I have driven to a town after having the turret of my tank disabled. I then use the hull machine gun to kill the town ack! - better than just giving up.