In this dev server, the ranks of various naval ships were shuffled around, and recently the ranks of some premiums increased to allow them to grind higher tier vehicles more efficiently.
However the U.S.S. Des Moines seems to be left out of both of these changes. As of the second dev server, it still sits at Rank IV and cannot research the highest capital ships in Rank VI (Note that its sister, the U.S.S. Newport News, is Rank V).
This change may especially be important because the U.S.S. Texas devblog includes:
but this is actually false, as the Texas is Rank VI and therefore cannot be researched efficiently by the Rank IV Des Moines.