The Navy decided to suspend the operation of the three newest 1,800-ton submarines early last year due to problems with their component parts, according to a lawmaker.

Rep. Song Young-sun of the minority Future Hope Alliance party told media that weak bolts used to fixate their upper bridges and decks were broken or loosened during their maritime operations on a number of occasions.

For the first 1,800-ton submarine Sohn Won-il, a total of 20 bolts came loose on six occasions between 2006 and 2009.

For the second submarine Jeong Ji, its bolts were broken or loosened on six occasions between 2009 and 2010 while for the third submarine Ahn Jung-geun, its bolts were broken and came loose on three occasions during the same period.

The 214-class submarines, which were designed by German’s Howaldtswerke Deutsche Werft AG, or HDW, and built by Hyundai Heavy Industries, are the primary naval assets for underwater operations.

The military investigated and found that a local subcontractor produced and provided bolts which were weaker than what the German firm required in its design of the submarines, sources said.

After the investigation result came out, the bolts were replaced with stronger ones, but the problems continued to occur, they said. HDW technicians came to Korea and fixed the problems from last June to February.

“After the problems were addressed, there are currently no problems in the operation of the submarines,” a Navy official said, declining to be named.

By Song Sang-ho (sshluck@heraldcorp.com)