The navy said its 1,200-ton submarine SSK Lee Eok Gi set sail from the country’s new Nava Port on Jeju Island today.
The 56metre-long and 5.5metre-wide sub is armed with Harpoon missiles, submarine mines and more than a dozen torpedoes.
It is capable of sailing back and forth between South Korea and Hawaii without fuel supply.
Cdr. Kang Byung-oh, the captain of the submarine, said: “[Submarines are] faster than ships and can carry out successive underwater operations for much longer.”
South Korea’s Nava Port can accommodate more than 20 warships and two 150,00ton cruise liners at the same time.
The navy also has nine other 1,800ton subs ready for launch, and plans to introduce 3,000ton subs in 2020.
In addition, South Korea hopes to introduce nuclear subs.
In a recent parliamentary session, South Korean Defence Minister Song Yong-moo said: “The time has come: we need nuclear submarines.”
The country’s show of muscle follow North Korea’s latest missile launch towards Japan on Friday.
South Korean President Moon Jae-in and US President Donald Trump have both agreed to put more pressure on North Korea through sanctions.
Blue House spokesman Park Soo-hyun said: “The two leaders agreed to strengthen cooperation, and exert stronger and practical sanctions on North Korea so that it realises provocative actions leads to further diplomatic isolation and economic pressure.”
North Korea’s missile launch on Friday was the second this month, following its sixth nuclear test on September 3.
After the launch, the state’s Korean Central News Agency (KCNA) released an article in which Kim Jong-un named South Korea as “traitors and dogs” of the US.
South Korea fired back with a final warning, saying Pyongyang will be “destroyed beyond recovery” if it fires another missile.
Mr Moon said: “In case North Korea undertakes provocations against us or our ally, we have the power to destroy (the North) beyond recovery.”
Mr Moon and Mr Trump have agreed to work with the international community to implement the latest resolution from the United Nations’ Security Council.
The resolution was adopted on September 11 after the council anonymously voted to step up sanctions agains the rouge sate.
The sanctions include a ban on textile imports and capping fuel supplies.