Seoul, May 8 (IANS): The North Korean submarine that fired a ballistic missile from underwater 24 hours ago was the one that had to be towed ashore due to an engine problem following an earlier missile test-firing in October last year, sources said on Sunday.

The North is believed to have repaired the Gorae-class vessel since the October 19, 2021, test-firing that also took place in waters off the country's eastern coastal city of Sinpo, where the North's main submarine shipyard is located, reports Yonhap News Agency.

Due to damage to its engine from the impact of the firing at the time, the 2,000-tonne-class submarine could not move on its own and had to be towed by a tugboat to the Sinpo shipyard, according to military and intelligence authorities.

"Though the extent of the damage was not exactly determined, it was not in a condition where it could move on its own. It had to be towed," a source said on condition of anonymity.

The North could have carried out the October firing in a hurried manner without much preparation as South Korea had successfully test-fired two submarine-launched ballistic missiles (SLBMs) the previous month, becoming the world's seventh country with homegrown SLBMs.

Sources said that South Korean and US intelligence authorities had detected signs of the North repairing the submarine until recently before the vessel was used in Saturday's SLBM launch.

No signs have emerged yet that indicate any damage to the vessel from the latest launch.

The Gorae-class submarine, which is 67 metres long and 7 metres wide, is believed to be the only type capable of firing missiles among North Korea's submarines.