Who Has What

From my IISS The Military Balance 2008, these are extracts of the order of battle:

North Korea

Ground forces
One armored corps, four mechanized corps, 12 infantry corps, two artillery corps, a capital defense corps, and 9 separate multiple rocket launcher brigades.  They also have nearly 90,000 special forces--mostly recon, light infantry, and snipers--not real special forces operators as we think of them. They get little training other than physical training, small unit drills, and farming during harvest. They are probably hungry a lot.

Equipment is old, with their 3,500 tanks getting to the point where they should be sitting outside of VFW posts. When your best stuff is either a T-62 or a Chinese copy of a T-55, you should chain your crews to the interior. More than 10,000 tube or rocket artillery form the basis of their best military strategy--threatening to turn Seoul into a "sea of fire." They have lots of anti-aircraft guns and mostly older surface-to-air missiles. They have some longer range missiles, as well.

There are about 45 reserve infantry divisions. I assume their quality would be poor in both terms of equipment and training. They might belong in the last category below.

Navy
They have 22 submarines plus 40 coastal subs, half quite small, that have questionable seaworthiness. Add in 8 frigates and corvettes and over 300 patrol boats, with only 10% having old missiles capable of hitting ships. They have a lot of amphibious craft that could be used to invade those Yellow Sea islands in the news of late and old shore-based anti-ship missiles.

Air force
They have 500 mostly elderly combat aircraft and 300 transport aircraft--almost all elderly biplanes designed to fly low into South Korea to drop sniper units. Their training is so poor that at best they could be used as a kamikaze force on a one-way mission (and how many of those one-way missions would involve pilots ditching at sea to hope for defecting is a good question). North Korea would do better to turn them all into jury-rigged cruise missiles.

Cannon fodder
Toss in 189,000 internal security troops that would be basically static light infantry and lots of militia theoretically capable of fighting but probably only useful for searching for downed US and ROK pilots.

South Korea

Ground forces
Ten corps with five mechanized and 17 infantry division plus two separate infantry brigades, seven special forces brigades (I assume these are more like rangers or paratroopers in quality, for the most part), one air assault brigade, and three "counter-infiltration" brigades. They will be of decent quality in training.

There are two marine divisions and one brigade.

They have about 2,300 tanks, with half being modern and the other half old but with better electronics, I assume, and certainly better training. Their infantry vehicles are reasonably modern. They have about 4,500 tube and rocket artillery. They have anti-tank and anti-aircraft weapons, as well.

Toss in 23 reserve infantry divisions. I imagine a lot would be used for rear area security to guard against the many "special forces" North Korea would attempt to infiltrate into the south. And there are 3.5 million civilian defence corps, which I assume are at best local defense forces.

Navy
Ten subs and a couple small coastal subs, 44 destroyers, frigates, and corvettes, 75 patrol boats, 10 mine warfare, and 50 amphibious ships and craft. South Korea's navy is growing to blue water capabilities.

Air power
They have over 500 combat aircraft from F-15s and F-16s to F-5s and F-4s, so it is a mixed lot. Electronics and pilot quality will be far better than the North Koreans, however.

60 attack and over 300 tranport helicopters are available.

United States

We have a mechanized brigade in South Korea as well as a couple brigades worth of attack helicopters and 100 or so F-16s and A-10s. These represent the tip of the spear, with naval forces and aircraft as far back as the continental United States capable of being flown in quickly. Air power will be the least of our worries.

Ground forces would take weeks to start arriving. Even a Stryker brigade would take a month to be airlifted (if we wanted to strip those planes from supporting the war in Afghanistan). But why bother since one could be shipped by sea in the same time? The Marines have a regiment in the western Pacific. Heavy forces would take the most time to move by rail from US bases to ports and then load up. Some could get there faster if we have prepositioned equipment in place. I assume we have at least a brigade's worth in South Korea and we'd have some stuff already afloat. I don't expect more than 4 brigades, mostly light stuff, could be in the theater in time for fighting if it is a bolt from the blue invasion by North Korea.

So there you go. Those are the combatants. Assuming China doesn't get involved. That's a whole new war.

Oh, and we have nukes and North Korea has chemical weapons. That's a whole new war, too.