Geoffrey Forden posted information on likely causes of the sinking of the South Korean frigate Cheonan before the formal report was released:
One of the “mysteries” surrounding the sinking of the ROK’s warship, Cheonan, is that the explosion split the ship in half, a result our popular culture has trained us to forget. After all, World War II movies always show a torpedo strike in the same way: one or two white streaks quickly approaching the ship followed by a localized jet of water where the torpedo struck the hull. Sailors stream out of their bunks to jump over the side as the ship keels over, taking in water. Below the water line, jagged holes, punched by the explosive force of the warhead, let in sea water. Compartments quickly (or if dramatic effect is needed, slowly) fill with water, drowning all the bit players, uh, sailors trapped below.
These movies have influenced our expectations for the damage caused by modern torpedoes even though there are much more efficient ways for a torpedo to destroy a surface ship. [. . .]
The second major effect damaging the hull, and probably the one that caused the vessel to break in half, was a jet of water blasting its way through the ship. This jet was formed as the gas bubble created by the initial explosion collapsed upon reaching the ship’s hull.
This is the way modern torpedoes sink ships. Everything about the Cheonan’s sinking is consistent with either a torpedo or submerged mine blowing up beneath the ship’s keel.
Fascinating though this is, the official report (as filtered through what was made available to international media) discounted this mechanism:
South Korean scientists at the Sound Engineering Research Lab of Soongsil University have performed an analysis of the acoustic signals (the media report mistakenly calls them seismic waves) associated with the sinking of the Cheonan. It would be very nice to see their actual analysis — and the data would be even cooler — but it appears on the face of it to be a very interesting result. Their main conclusion, again based solely on the media report of their findings, seems to be that the Cheonan was actually struck by a heavy torpedo. (The say the most likely candidate is the Chinese Yu-3 heavy torpedo with a 205 kg high explosive warhead.) According the article, the South Korean scientists believe the torpedo struck the hull of the Cheonan but since the explosive is significantly aft of the torpedo’s bow, the center of the explosion was a little over 2 meters away. They rule out the “kill mechanism” being a bubble jet.
Interestingly, a summary in New Scientist (which is where I found the link above), seems to have been written before the updated information was added to the original post, as it attributes the sinking to the “deadly bubble jet”.