I had to boost the difficulty of the game because if you played smart and reached 100% bonus, you basically could not lose as the cannon could shoot down enemies before they had the chance to get in position, to help with the difficulty I've added the EMP that used wisely could help progress... Repairing the damaged wagons and smart target choices are essential, but for sure I could have made the exit cannon a bit clearer, I assumed that using spacebar to get in would be enough to assume spacebar to get out :-D