China's recent deployment of a nuclear submarine for an antipiracy mission in the Gulf of Aden may have caused unease among its neighbours, but naval experts say the Type 091 vessel is unlikely to pose any real threat because of the noise it generates. The experts say the international community should instead keep an eye on China's quieter, more advanced diesel-driven submarines. CCTV's military channel last Sunday reported that a nuclear submarine from the People's Liberation Army Navy had completed a two-month escort mission in the pirate-infested waters of the Gulf of Aden, and returned to its base in Qingdao , Shandong province. The report did not specify the type of submarine used, but commentators said the footage suggested it was an updated version of a Type 091 submarine. It was the first time state media had confirmed China was deploying nuclear submarines for anti-piracy missions in the seas between Yemen and Somalia, although it had long been suggested by overseas media. "CCTV's report … shows that the PLA Navy really wants to improve its transparency in answer to US criticism [that it was not being transparent enough]," Macau-based military expert Antony Wong Dong said. "But the key reason that pushed the PLA Navy to increase its transparency is because the Type 091 subs are so easily detected by the US navy, although CCTV did not report this." The Type 091, which the US calls a Han-class submarine, is designed to seek out and destroy enemy vessels in deep waters. A March 2007 issue of Seapower Magazine - an official publication of the Navy League of the US - referred to such vessels as "relatively noisy submarines based on 1950s and 1960s technology", although it admitted the models had benefited from several upgrades over the years. Belgian naval analyst Frederik Van Lokeren wrote on his blog that the Type 091 had "no combat value and can only be … used for training purposes". But Beijing-based naval expert Li Jie said China had spared no effort to reduce its noise problem, developing several improved versions over the four decades since the first generation of the nuclear submarine was launched in December 1970. "The PLA Navy now has Type 092, and 093 and 094 ballistic-missile subs that are more advanced than the Type 091 series," Li said. "The navy's trials in the past two decades showed that Type 091 subs were not as noisy as the US media described, although we should recognise that the decibel level of the Type 091 subs is not as [low] as US samegeneration vessels like USS Ohio nuclear subs." Li said even though they were about 20 years behind US vessels, the Type 091 submarines still posed a threat to US aircraft carriers. During the 1996 Taiwan Strait crisis, two PLA Navy Type 091 submarines tracked two aircraft carrier groups led by the USS Abraham Lincoln and the USS Independence. He said they pushed the US carriers back 200 miles. Macau-based naval expert Wong said while China's more advanced Type 093 vessels had yet to overcome their noise problems, the PLA Navy's diesel-electric submarines had achieved an advantage that could pose a significant threat to the international community. "China's diesel-powered subs have reached international standard … They are equipped with air-independent propulsion and can remain silent during underwater ambushes," Wong said. In October 1995, a Type 039 Song-class diesel-powered submarine sailed close to the USS Independence carrier group without being detected by the US navy until it suddenly surfaced from the waters near the Taiwan Strait, according to a documentary broadcast by Guangdong Satellite TV last month. The elusiveness of Type 039 vessels has helped China increase its share of the weapons market. Last month, Pakistan's media reported that the country would buy eight such submarines for US$5 billion, making it China's largest single sale of submarines.