Enable developer console and press ` tilde (default button to bring up console) After that, make sure to input the following commands:
Replace number with a desired amount. I recommend setting health to 50000 and hornet count to 5000.
This way you will be able to fly through the missions and ultimately get xp.
Note: If the cheats do not work, enter the console sv_cheats 1 code before entering these codes.