I've made it a habit to go through the game, every challenge and every battle, including the intro, I'm getting through it now in 3:20 (best time 3:11). Looking at where to improve times, I'd like to do #14 faster.
Other posts mention flying through the factory and taking out the tanks...
If you find extra content, or a game that continues SWON, please post. I've looked through Google at length, and can't find a follow-up game, or expansion for the PC game.
It looks like they left it wide open for a follow up when, at the end, Kreiger gets away, and it's just D-Day.