U.S. keeps close watch on North Korea as threats continue

(CBS News) -- The U.S. Navy is moving radar and anti-missile systems towards North Korea -- part of a military build-up after belligerent threats from North Korea's new dictator.

Thirty-year-old Kim Jong Un took over from his late father just over a year ago and he is not the first North Korean dictator to threaten war with South Korea and its American allies.

But this time is different. South Korea's new President Park Geun-hye is dealing with a new political reality.

Retired general Walter Sharp says the South Korean people have stated they're not going to stand for this anymore.

Sharp, former commander of U.S. forces in Korea, says another incident like the 2010 shelling of a South Korean island would trigger not just a tit-for-tat retaliation but a combined attack by U.S. and South Korean forces.

"Things have changed since November 2010 and if he does another attack like that, the response is going to be swift and it's going to be strong," said Sharp.

Sharp began the retaliation planning after the 2010 shelling in which the north fired about 170 rounds, killing four South Koreans.

The Seoul Government was criticized for a weak response and the U.S. and South Korea began preparing a much tougher retaliation for the next time.

"What should we do to be able take something of value to Kim Jong Un and hold that at risk?" said Sharp.

"There are things that North Korea has, in the past, really valued. Where they have put their money into their military forces? They put it into nuclear facilities. They've put it into ballistic missiles."

For now, the U.S. is making a point of showing off all the firepower it could bring to bear. Everything from F-22 stealth fighters to B-2 stealth bombers, flying into and over South Korea.