Seoul, South Korea (CNN) -- South Korea conducted its largest-ever nationwide civil defense drill Wednesday afternoon to prepare the public for a potential military attack from North Korea after Pyongyang shelled a South Korean island less than a month ago.
"After the bombing, we believed it was important for the public to know where to take shelter since the South is within five-minute-distance from a North Korean air raid," Kim Kwang-hee, the director of civil defense said.
The drill involved 12 fighter jets which flew over the airs of Seoul and the country to mock an enemy air drill. More than 250,000 public workers helped civilians take shelter in underground facilities and subway stations, according to the National Emergency Management Agency (NEMA).
Traffic was stopped all across the country, and students were escorted out of school buildings into underground locations. Office workers were asked to move into basement parking lots for cover.
Civil defense drills take place on a regular basis and in the past have been ignored by many.
However, the threat of war is felt at a greater degree after North Korea shelled the South Korean island of Yeonpyeong in November which resulted in the death of four people.
"We actually don't participate very well, because nothing happened between North Korea and South Korea. But recently it has happened, so it's very serious for us to think about these kinds of events," said Chung Woo-sub, a university student.
South Korea plans on boosting its underground shelter facilities along the border regions and in the island areas in the Yellow Sea where the island attack occurred, according to NEMA.
Also the Defense Ministry announced Wednesday that it has nominated Gen. Kim Sang-ki, commander of the Third Army, for the newly vacated post of South Korea's Army chief, Yonhap news agency reported.
Gen. Hwang Eui-don, the former chief of the Army, resigned this week after being accused of using insider information to make money off of a property investment, Yonhap reported