The USS Valdemar (NCC-26198) was an Ambassador Class Heavy Cruiser in service in the 24th century. In 2333, the Valdemar was under the command o Captain Calabrese. TheValdemar was part of the task force organized to fight an unknown vessel attacking Federation vessels. In 2370, the Valdemar, the USS Prokofiev and the Enterprise D were sent to the Cardassian border after Chief Miles O'Brien was arrested on false charges.