Super sorry about that, now when you beat the first level, it brings you to the second one! Half the levels were skipped on the version you played due to a BAD bug, and now you can get to the level that teaches you how to glitch through walls. There is actually a powerup called wings, which makes WASD direct the tank as you describe. There is also now a difficulty option in the settings menu, but I think when you played it the fact that half the levels were missing made the difficulty curve brutal. I have fixed these issues, so I would be happy if you checked the new version out! Thanks for the feedback, I wouldn't have found the missing levels so fast if you hadn't said something!
tldr: whoops half the levels were missing, and they taught you how to glitch through walls