1942 is the first in Japan Capsule Computers (Capcom)'s series of three vertical-scrolling airplane shoot'em ups. The second game in the series is 1943, which has similar but rather more advanced hardware than 1942, and the last game in the series is 1941, a MUCH more advanced game which runs on the CPSII game systems (shared by most of the Street Fighter series).
The action is fairly samey; lots and lots of different little airplanes come in from all sides of the screen, and you have to shoot them. There are a few powerups; four bullets instead of two, smart bomb, and two "side-car" planelets which make your sprite at least twice as wide as normal, and hence easier for the enemies to hit. There are also a few powerups which don't seem to do anything other than get you a few points.
1942 runs on two Z-80A CPUs, and it uses two AY-3-8910 PSG chips for audio output. The board (mine is an original Capcom) is very sensitive to the state of the +5V rail - 0.10 volt too low and at best you'll have flickering in the background layers; at worst, you'll have completely wrong colors (like green sea!). Hardware-complexity-wise, the board is somewhere between Ghosts'N'Goblins and 1943. It has only one background (scroll) layer and a large number of objects, plus a text layer on top.
1942 uses a vertical low-res monitor, one or two 8-way joysticks with two buttons. The pinout is below. The Capcom PCB part # for this board is 84100.
DIP Switch Bank A
DIP Switch Bank B