This game has unused graphics.
Made before the days of microprocessor-based arcade games (though the enemy graphics are on a PROM chip), Anti-Aircraft is a very simple shooter. Shoot one or two ships at a time and...well, that's it, really.
While the enemy ships that cross the screen are normally bombers, there's an unused UFO design in the game. Pin 14 of the 003127 IC (a PROM located at grid location K1) is tied to ground, but also has a pull-up resistor. Cutting the ground trace causes address bit A4 to be pulled high, selecting the UFO data.
...Or just use DICE and change that in the pseudo-Dip Switch menu.