Currently, the missions give out specific ships, and while the nature of the Empire espouses this, from a game standpoint, it is not that fun.
What I propose is this; that there be an before mission requisition phase.
Each imperial ship has value assigned to it, represented in either hits and/or crits. To requisition this ship, you roll a number of red dice equal to your pilot skill (these rolls cannot be modified by abilities/talents).
As a default, the standard TIE Fighter is ALWAYS available, and is the default.
A TIE Bomber may require two hits to be rolled. A TIE Punisher may require 3 hits and 1 crit (values must be evaluated, likely based on ship costs)
The idea is as you increase in pilot skill, you will potentially get access to more deadly, and durable, TIE craft.
Also, and this will require much fine tuning, will be a Medal system. If you accomplish certain things in the campaign, you earn medals. These medals offer bonuses to your requisitioning.
Examples include a medal that gives you a bonus for each mission you are not shot down in.
Each mission not shot down equals re-roll that many requisition dice.
Here is the proposed requirements:
TIE Fighter - Automatic
TIE Bomber - 2 hits
TIE Interceptor - 3 hits
TIE Defender - 2 crits, 4 hits
TIE Advanced - 4 hits
TIE Punisher - 4 hits
TIE Aggressor - 2 hits
TIE Striker - 3 hits
TIE Advanced Prototype - 2 hits