SOS

SOS is the third of three monochromatic arcade games that were released by Namco in early 1980 - the first two were Navalone and Kaitei Takara Sagashi (which was originally created by K. K. Tokki as a prototype). It is a fixed shooter in which the player must use a 2-way joystick to direct a fighter plane known as a "Shinryaku" across the bottom of the screen, while enemy planes fly down towards it from the top of the screen. You can press the Firing Button to make the Shinryaku fire a bullet from its nose at the enemy planes to destroy them for 10 points apiece, but you can only fire one bullet at a time - and if you miss, you will have to wait for the bullet to go off the top of the screen before you can try again. Occasionally, a flashing arrow will appear to point at either the left or right side of the screen while an "SOS" signal is sounding in Morse Code - and if you manage to make it to that side of the screen before it disappears, you will receive 30 points and eliminate some of the enemy planes that have bypassed your Shinryaku. If the number of enemy planes that have bypassed your Shinryaku amounts to 100, the game will immediately end regardless of how many lives you have remaining.

Controversy
One of the reasons this game is infamous is because of the "coffee breaks" it takes after every 2000 points, depicting a young woman. On the first two times, she will be wearing a bikini - but if the arcade owner has set the "nudity" opt dip switch to "on", she will be topless after 6000 points and completely naked after 10000 points.