> It's theoretically possible to build up so many extra cities that you can actually take a 30 minute break in the game

It's not only possible, it is fairly routine for good players. This is because of an interesting bug in the game which has a big effect on the skill progression of developing players.

The bug is commonly called the "810" bug, because on most machines it occurs when you get 810k points. It actually occurs at 800k + B, where B is the score that gives a bonus city, but 10k was by far the most common setting for B [1]. Hence, "810" bug.

What the "810" bug does is give you a huge number of bonus cities--something in the neighborhood of 170. Even if you just barely made to 810, with 170 cities you've got around 20 minutes of play even if you never save another city.

The typical progression of a developing player went something like this. Your first few games are overwhelming, and you die quickly. After a while, you are reaching the 6x stage (Missile Command has 6 levels of difficulty. It starts with, if I recall correctly, 2 stages of 1x, then 2 of 2x, then 2 of 3x, and so on, until you reach 6x, which is the top difficulty).

Once your games start regular reaching 6x, you go through a long stage of steady improvement, as you get better at 6x play. Things are still going pretty fast for you, and you have to rely on some probabilitic play. For instance, at this stage you probably heavily rely on using one of your slow side bases to lay out a line of missiles after you see the first incoming wave. You aren't really aiming at specific targets--you are trying to lay down a fence basically that will catch much of that incoming wave. Then you use the fast center base to deal with any smart bombs or any missiles that got through the fence that you don't think you can take with a side base. Then, if you haven't panicked yet and thrown away the missiles from the other side base, you do another fence to try to catch the second incoming wave.

When you are down enough on cities that you only have 2 or 3 at the start of stage, you probably switch to concentrating on saving those cities, so you depend less on making a missile fence, and more on trying to pick off specific targets that are coming to the cities. In particular, you are probably trying to make sure to save a city next to the center base, to make sure you stay alive.

You get better and better, so that you keep six cities on the ground, and even build up some in resevere, for longer and longer, and you start to put more thought into your missile fences--you start being able to recognize as soon as you see an incoming wave where there will be convergence points, and your fence starts to become not a solid line, but a few well placed obstacles.

Then the day comes when you manage to hold on long enough to reach 810. Your reward is at least 20 minutes in which you get to play 6x and cannot die. You can practice precise targeting, or practice making perfect fences, or practice using your side bases for things you would normally use the center for.

This practice is very fruitful. Next time you play, you will find you are noticeably better. You might not get to 810 on the next game, but you will in the next few games. And then after that practice, you'll find the gap to the next 810 even lower. Sometime in here, you'll find that you can regularly reach 810.

Now you start to get really good. All those immortal practice sections let you get to where you can pick off anything with any base, and you never need to use a missile fence because you can quickly see where to place the minimum number of shots to kill everything on the screen.

You will soon reach the point where you regularly get to 810 with 6 cities on screen and 70+ cities in reserve, so when you hit 810 and get the bug's bonus, you have around 250 cities. Congratulations, you are now at the "walk away and the machine plays itself for half an hour" milestone.

I don't recall for sure, but I think when you wrap the machine you hit another bug that gives you a bunch more cities. There's also some point in there, maybe on the second wrap, where the machine gives you two waves labeled 0x, where everything comes down real fast and you don't have any control, and then the machine starts over at 1x, but you still have whatever bonus cities you had left.

When you've reached this stage, the only limit to how long you can play Missile Command is your endurance and any bugs farther along in the game. Many players at this stage would just play to 810 (just to maintain their skill) and then walk away to go play some other game. I had a kid follow me around all day once picking up my Missile Command leftovers [2].

If you were lucky, an arcade in your area had a Super Missile Attack. That was a third party hack that modified Missile Command to go to 10x, and added an orbital laser platform. We had one in my area for a short time, and none of the Missile Command players (who all could 810 with essentially no cities lost on the way to 810) got past 100k on Super Missile Attack. It was wonderful.

Unfortunately, it was also very very rare. The company that made it was sued by Atari and stopped making them. (It worked out for them, though...Atari was impressed enough to hire them to write a couple new games).

[1] I think I only encountered a non-10k machine once. There was an arcade in Pasadena, California on Colorado Blvd named Pak Mann Arcade. It was a pretty good arcade. I went their one night a day or two before the Rose Parade, when Colorado Blvd is already full of people camping out for the parade. Pak Mann cranked all the games up to their hardest settings, so they had the Missile Command at 20k bonus. Even more brutal was Defender. Not only was it 20k bonus, and a couple less starting ships than normal, as soon as the first wave spawned, they went straight for the humans at high speed, and in about 10 seconds your planet was gone and you were in a space wave. Me and my friends were all "can play forever" Defender players at the time, and none of us got past 30k that night.

[2] Senior Ditch Day, Caltech, 1982. As a senior, I had to stay off campus all day. I went to an arcade and started playing Missile Command. Some kid, maybe 11 or 12, was watching. I hit 810 and immediately walked away to go play Defender. The kid happily jumped on the Missile Command to get some 6x practice. A little later, I left to go to another arcade. I noticed the kid was following me, at a respectful distance, trying not to look like he was following me. At the next arcade, I went to Missile Command, and the kid took up a position where he could watch. I 810'ed and walked away to play something else. The kid again took over. Long story short (too late, I know!), that kid followed me all day, to benefit from my Missile Comamnd leftovers.