The K721 naval mines intended to thwart enemy warships exploded properly only one in six times during tests. That is a success rate of only 16.6 percent.
According to a government source on Tuesday, the K721 or "Jamryong" mine exploded on contact in only three of seven tests conducted in 2007 and 2009.
The Board of Audit and Inspection asked the Defense Agency for Technology and Quality to test the mines again in September of last year, and all six tests failed.
In a second test in January this year, the mines went off only six times out of 30.
Each of the mines costs a staggering W170 million (US$1=W1,061) and the Navy has procured around 200 since the late 1990s.
There are both magnetic sea mines, which explode when sensors detect changes in magnetic fields as a ship passes by, and acoustic ones that blow up when they detect sounds. The K721 was designed to do both.
A DATQ official said the K721 operated normally in tests on land but "may not explode under water due to the speed of undercurrents and other external factors."
The Navy pledged to conduct more detailed tests soon. It claims there were "unforeseen variables" in the trials in January, such as the vessel used in that test failing to create a strong magnetic field or the vessel being too small for the mine’s intended specifications.
The K721 was developed jointly by the Agency for Defense Development and LIG Nex1, which manufactured them. The company also makes the submarine torpedo Hongsangeo (Red Shark). The military will decide next month whether to order more Hongsangeo torpedoes.