The navy has stated a requirement for six units .
That was established before navy decided to convert four Ohio - class ballistic - missile submarines to guided - missile submarines ( SSGNs ) with the additional mission of support of special operations forces .
The navy has stated a requirement for six units , but that was established before it decided to convert four Ohio - class ballistic - missile submarines to guided - missile submarines ( SSGNs ) with the additional mission of support of special operations forces .