Game features unlocking at ranks:
#1 - Callsigns button (symbol you can place on your ship).
#2 - Special item slot (hacking tools etc.).
#3 - Shield slot.
#4 - In-game chat (press Enter and type your message for all players).
#5 - Second ship.
#6 - Rewards button.
#8 - Second weapon slot.
#15 - Third ship.
#16 - Missiles slot.
#20 - Fourth ship.
#21 - Second missiles slot.