The US has begun building its most advanced Columbia-class nuclear-powered ballistic-missile submarine (SSBN). The USS District of Columbia is the first ship in the new class of SSBNs built for the US Navy by General Dynamics Electric Boat (GDEB). Reports say that GDEB signed a contract of over US$10 billion for the first two Columbia-class boats in 2021. According to reports, the keel-laying ceremony for the USS District of Columbia took place on June 4. The event marked the ceremonial start to the construction of the first in a new class of ballistic-missile submarines.