New ships and weapons and misssions become available as you successfully finish each mission.
There is a total of 4 (plus one bonus ship) ships to play with and 5 weapons to use, and 16 missions to play (not to mention about 60 emails to browse through).
However, just like in 90% of games these will have to be unlocked by successfully completing the missions to continue advancement in the game.
But.. if you do want to spoil the whole element of advancement through the game and the story, there IS an easter egg in the game that will unlock all of the missionas, ships and weapons to you
I'll only give the hint that it involves the pilots name when adding a new pilot