Successfully complete the game, then load the cleared saved game. When you purchase three Sovereign class ships, the U.S.S. Legacy will be the final ship.
Achievements
Accomplish the indicated achievement to get the corresponding number of Gamerscore points:
Starfleet Academy Graduate (25 points): Complete the Tutorial Mission.
Captain Archer Award (50 points): Complete all missions in the Enterprise era.
Admiral Kirk Award (50 points): Complete all missions in the TOS era.
Starfleet Ensign (50 points): Complete the single player campaign on "Ensign" difficulty.
Starfleet Captain (75 points): Complete the single player campaign on "Captain" difficulty.
Starfleet Admiral (100 points): Complete the single player campaign on "Admiral" difficulty.
T'Pol Award (30 points): Complete the Enterprise era without losing a single ship.
Spock Award (35 points): Complete the Original Series era without losing a single ship.
Riker Award (40 points): Complete the Next Generation era without losing a single ship.
Guardian of Epsilon Theta (20 points): Protect all the medical ships in "Be My Shepherd".
Protector of Encaria (20 points): Keep the poisonous spore count low during "Poisoned Well".
Tyburn Shockwave (20 points): During "Stirring the Hive", knockout as many of the enemy fleet as you can in one blow...
Lone Wolf of Makus (20 points): Complete mission objectives in "The Squeeze" without the aid of starbases.
Liberator of Makus (20 points): Secure all enemy strongholds in "The Squeeze".
Pacifist of Makus (20 points): Complete "The Squeeze" without spilling any blood...