Several sources have stated if war breaks out, the entire conflict would be over in about 24 hours. With the U.S. and South Korean Forces taking full control over the North. One of my personal questions is whether China may or may not step in and attempt to "police" part of North Korea. So as to prevent a U.S. friendly country becoming China's neighbor.
Some people seem to believe the North's sheer military numbers would overwhelm any opposition. However consider the first Iraq War. That was the first time Western powers had fought a full scale war against a nation using relatively modern Soviet Era technology (1970s-1980s). Saddam had something like the 4th largest army in the world, and was expected to inflict a high level of casualties on the Coalition. However that technology/numbers proved almost worthless against the majority of what the coalition was fielding (A great example would be the Battle of 73 Easting, in which the equivalent of an Iraqi Brigade was destroyed while the Coalition only lost 1 soldier to enemy fire.)
North Korea's Military is comprised mainly of 50s-60s Soviet equipment. I won't take into account their air force as I consider they would lose the ability to launch attack craft almost immediately after war is declared (Cruise Missiles would be one method of destroying runways preventing planes from taking off. Air Superiority Fighters/Anti Aircraft Sites would quickly knock out any North Korean planes which made if off the ground). Their attack helicopter fleet is also incredibly small, estimated at only 20 Mi-24 Hinds.
Their Navy is small, the only noteworthy attack craft here are Patrol Boats, Missile Boats, Torpedo Boats, and around 35 small Submarines. Neither of these pose much of a serious threat.
As mentioned before, their army is severely underpowered. Most tanks are either Type 62s, or Type 54/55s (Which are all outdated). They may have some tanks which possess capabilities similar to the Russian T90, but not much is known about these (nor how many are fielded). North Korean Artillery could cause some damage to South Korean cities, but these would quickly get destroyed. Small arms consist of old Ak-47s, AKMs, RPGs, and not much else.
The only way I suspect North Korea could cause massive casualties against an invading force, is if they detonated an immobile nuke. Of course this is unlikely to happen given how quickly North Korean positions would be overrun. The time required to set such a plan into motion would likely take a great effort in preparation.
The idea of war is not to die for your country, it's to make the enemy die for his.
Former Member of the VOC
IRON STATS Wars Fought: 13 POWs Taken: 2 Nations ZIed: 2 Aid Given: $341 Million
Recruits: 7 Alliances Fought: LSF, Sparta, VE, Umbrella, DBDC, STA
Alliance Seniority: 2,595 Days Soldier Casualties: 867,426 Att + 2,123,326 Def = 2,990,752