North Korea has been building a new high-speed, wave piercing craft to deploy them front-line troops as part of efforts enhance its infiltration capabilities through sea routes, a military source said Sunday. Pyongyang has been building a Very Slender Vessel (VSV), which can move over 100 kilometer per hour with a small number of special forces aboard. The cylindrical vessel is about 10-15 meters long with a small-cross section that can pierce straight through waves. The VSV is much faster than air-cushion vehicles deployed by North Korea, which can move at speeds of up to 96 km/h. The communist state has deployed about 70 air-cushion vehicles on its west coast and 60 of the amphibious vehicles in the east at its four hovercraft bases, according to a report by the South Korean Joint Chiefs of Staff. "North Korea has been constructing the very slender vessel since last year to enhance its commandos' maritime infiltration capability," the source said, asking for anonymity. "This is believed to be ready for deployment."    The ship was first spotted in satellite imagery last year when Pyongyang conducted its first test run in the East Sea, the source said. Seoul officials consider the high-speed craft as a big threat to front-line islands, especially after the North torpedoed South Korean Navy's Cheonan warship in the tensely guarded western sea three years ago, killing 46 sailors on board. "North Korea has continuously stepped up its maritime infiltration capability since the Cheonan sinking, and production of the high-speed craft is believed to be part of its plans to build up its capability," a senior military official said, asking not to be named. "If the VSV is deployed, it will be a big threat (to South Korea) along with the midget submarines that have already been in operation."    The new vessels are expected to be forward deployed in the eastern coast, the official said, raising the possibility that the North may paint them with stealth paint to camouflage its warships. The communist nation has regularly carried out landing operations using amphibious vehicles, which Seoul officials believe are aimed at infiltrating the inter-Korean sea boundary to quickly occupy South Korean border islands in case of war. When inter-Korean tension was running high last spring, North Korea's leader visited the bases on its east and west coast, and observed amphibious landing operations involving the hovercraft. The North Korean Army has also upgraded main battle tanks, deploying about 1,000 tanks equipped with improved armament in troops across the nation. The Songun-ho, named after the North's military-frst policy, features 800 to 900 meter thick walls, newly equipped with 93 mm-round thermobaric rocket launcher and SA-16 surface-to-air portable missiles, according to military intelligence. The tank's rocket launcher is believed to have been modeled after Russia's RPO-A recoilless flame thrower, with a maximum rage of 1 km, which can destroy personnel and weapons inside variousprotective shelters with high-explosive and thermal effects.