Is the transition to the new Columbia-class leaving a dangerous gap in naval defenses? Here's What You Need to Remember: There may not be enough overlap between the retirement of some of the Ohio-class submarines and the construction of the new Columbia-class. The U.S. Navy now has as many as fourteen Ohio-class nuclear-armed ballistic missile submarines and has already begun to build a new fleet of advanced, next-generation Columbia-class boats to replace them, yet the pace of their arrival raises the question as to whether there will be enough nuclear-armed undersea boats in the coming decades. The new Columbia class, which at the moment will likely consist of twelve boats, is expected to be fully delivered by 2042, arriving at a pace of one per year from 2033 through 2042. The Ohio submarines are maxed and taxed, meaning they have already greatly exceeded their expected service life and been tasked with continued functionality for years beyond what was planned, thus underscoring the heavily emphasized need to fast-track and prioritize the arrival of the Columbia submarines.