While the exact new features of these 2 SSKs remain predictably shrouded in secrecy, some PLA enthusiasts have speculated that the new SSKs will include new sonar and surveillance systems, some have even speculated that the newest models will be capable of vertically launching cruise missiles from their lengthened sails - the most noticeable new feature of the latest 2 Yuan Class SSKs being constructed in Wuhan. It is also widely believed that the Yuan Class SSKs include air-independent propulsion systems on board (as subtly implied by a PLA Daily article dated 23 Oct 2009), allowing for quieter patrols of longer endurance.