is a quite old game, made by Greg Kuperberg and released in 1982 under the Orion Software label. It was a PC Booter game, and even featured joystick support. It's one of those games with simple premise, simple graphics, but furious and fun gameplay.
The player controls a turret at the center of the screen, while planes go over it, pouring paratroopers and bombs. The turret cannon can be rotated left and right, to destroy the planes, paratroopers, or the hard to hit bombs. If paratroopers get to the ground alive, they'll try to enter the bunker where the turret is placed, and for that they need four men. That's the game over.
Special bonus happens if you hit the parachutes, making the men fall their death. Black humour gaming in 1982, perhaps? Another mechanic of the game, and very interesting, is that you can shoot as many bullets as you want, practically ensuring no man alive will touch the ground, but each bullet costs 1 point. So you can stay alive, but have a score of 0. So you must save the bullets and use them properly through the ever increasing difficulty.
And that is the game, really can't say much more. However, the gameplay is well balanced, and can get you hooked for a while. It was a refreshing change back in the day, specially seeing the lack of game possibilities the PC had in its only second year as platform.
Despite the basic graphics and simple gameplay,is still fun to play, providing fast action and challenging gameplay. A retrogamer reviewing important DOS games named the best DOS game ever, in a YouTube video I can't locate right now. Well, I think that's exaggerated, but you'll be surprised yourself if you never tried this game and got addicted.
Maybe today the game would even be labeled “casual”, but I suggest you to play it yourself for a while before thinking I'm going overboard with such a small game. Try it at The Internet Archive.