even if he is magically immune to being pierced or burned, pure concussion from shockwaves from hi explosives should break bones and rupture him internally. fly by wire, or targeting missiles should find any vulnerabilities (loose or missing scale). it shouldn't take long to bring him down once the surprise of his appearance and tough defenses are ascertained. as his target is likely Fort Knox, the Army (Fort Campbell) and Air Force (Wright-Patterson) will be there in short order and will be carrying the ordinance to deal with him after the Knox forces give their initial contact reports. even if Knox is defeated, Smaug will be trying to evaporate all the water that flooded the gold vaults (final security procedure) and that'll occupy him and perhaps tire him and make him more vulnerable when the reinforcements arrive.
