North Korea is being as clear as a bell with this. A few days ago, 3 or 4 Nork submarines, left their bases, almost certainly along the route the ballistic missile is intended to take, likely also with orders that if a ship fires on the missile, to attack it.
http://mainichi.jp/english/english/newsselect/news/20120405p2g00m0in095000c.html
Additional information:
At 370 tons submerged, the Sang-O class submarine has two 533mm torpedo tubes fitted with Russian 53-65KE torpedoes, and is capable of mine laying.
The 53-65 torpedo family are Russian made, wake-homing torpedoes designed to destroy surface ships. The 53-65KE is the exported version.
Instead of using active or passive homing as other torpedoes do, the 53-65 torpedoes use wake homing, which, upon finding the wake of a ship, turns to follow the wake to guide itself to the ship. The torpedoes have no way of telling which way the target ship is headed when they reach the wake, so they aren’t as effective as other means of homing.
To date, there have been no reports of a countermeasure that can confuse these torpedoes, making them very successful when they do home on to a ship.
Thus, I highly recommend to the US Navy that their guided missile ships in position to shoot down the Nork missile must have anti-sub assets available, and if they intend to shoot at the missile, to blow the Nork submarine out of the water FIRST.
Any and every Nork submarine at sea should be considered imminently hostile right now and subject to attack without notice.
North Korea doesn’t have a blue water Navy. All our Navy has to do is stay out of their operating range.
Our range will be great enough to deal with the problem, if needed. And the Norks will be too far away to do anything. Well, anything to us... excepting our USFK forces.