Zumwalt's likely service life and hypersonic refit

Will the Zumwalt class last in US Navy service, and is replacing its guns with hypersonic missiles sensible?

Long service is expected, with a preference for replacing one gun with hypersonic missiles while retaining the other.

The Zumwalts are expected to remain in US Navy service for a considerable time because they do not share the same problems as the littoral combat ships. At the time of this conversation, the third ship is described as not yet really having entered service. One preferred refit would replace one gun with hypersonic missiles and retain the other. The same proposal calls for more ships on the Zumwalt hull, including an air-defence variant.