The South Korean military has a credibility problem. That's because when Yeongpyeong Island was shelled by North Korean rockets on the 23rd, it took the South Korean self-propelled 155mm K-9 guns on the island 13 minutes to begin returning fire. The South Korean guns fired 80 rounds into North Korea before they were ordered to cease fire at about 3:30 PM, an hour after the North Koreans began firing. The North Koreans had fired 170 122mm rockets at Yeongpyeong, with about half the unguided rockets missing the island and landing in surrounding waters.
The credibility problem arose from the fact that North Korea had fired towards Yeongpyeong Island last January, but the shells from their coastal artillery landed north of the island. It gave everyone a fright, but there was no damage or casualties. The problems arose when the South Korean generals were called before parliament and asked what would happen if the North Koreans actually fired on Yeongpyeong Island. The reply was that South Korea guns on the island would promptly fire three or four times as many shells right back. That was a reasonable statement, if the North Koreans used their 130mm coast artillery weapons. These have a low rate of fire, and there aren't that many of them in the vicinity of the island. But the North Koreans moved up several 122mm rocket launchers, and let the island have it, and then quickly moved before the return fire arrived 13 minutes later. The South Korean generals had told parliament that return fire would begin within minutes, and the K-9s were prepared to do that. But first they had orders to call headquarters and ask permission to commence firing. That took most of the 13 minutes, as alarmed officers and officials at defense headquarters debated what to do. Firing artillery into North Korea could start another war, and no one wanted to be responsible for that.
The South Koreans also sent some fighter-bombers to the scene, including the new F-15K, armed with smart bombs. But these were ordered to stay out of North Korean air space, as an air attack might have escalated the fighting. However, the military was criticized for that as well, because the voters are in an uproar over the state of South Korean defenses, and the performance on the 23rd did not inspire confidence. In the long run, the military will probably be proven right to be prudent, but in the meantime, they have to be careful what they promise the politicians in public.