There is a documented option available that switches the planes into UFO's (see video).  Pin 14 of the 003127 IC (a PROM located at grid location K1) is tied to ground (at Pin 8 of K2), but also has a pull-up resistor. Cutting the ground trace causes address bit A4 to be pulled high, selecting the UFO data. A jumper can be installed to easily switch back and forth between planes and UFO's. The UFO version of the game was probably never released.




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