Use the following trick to get the U.S.S Voyager as a usable ship during Campaign mode. Buy three Intrepid class ships. Notice that none of them are named Voyager. Sell the last ship you bought then re-buy it. More than likely, it will be named with the same name. Do this about four to five times quickly and you will find the U.S.S Voyager. This is the only way to get it as a usable ship in Campaign mode. For it to actually have Kate Mulgrew as its Captain's voice, you must have luck.