Seoul, South Korea CNN —North Korea claims to have launched a new “Korean-style” tactical nuclear attack submarine that it says heralds “the beginning of a new chapter” for its navy. North Korean leader Kim Jong Un attends what state media report was a launching ceremony for a new tactical nuclear attack submarine. According to the Nuclear Threat Initiative, North Korea already has 20 Romeo-class subs in its fleet of an estimated 64 to 86 submarines. All US Navy submarines, both of the attack and ballistic missile varieties, are nuclear powered. The events also come amid signs that Pyongyang has been rattled by increasing cooperation between the United States and South Korea.