At the title screen, on the 2nd controller, hold the A button and press Right 9 times, Up 2 times, Left 2 times & Down 9 times. If done right, a series of numbers will appear on the top. Change them to the numbers below using Left/Right and A/B on controller 2 and then press Reset to enable the cheats. The codes can be combined too.
Shortly after you reach the first set of spinning walls, you'll reach a lake. If you dump bombs into the lake, a flag with an ''S'' on it will appear. Flying over the flag will give you a free ship.
Just before you get to the Fortress pause the game. Unpause the game, but instead of sticking around to fight the Fortress, you'll be able to just move right past it!