As I wrote in the last article, the machine was a successor of the Whirlwind computer, the world's first computer with real-time processing capability. It ended its role in the Lincoln Laboratory when a more powerful computer called TX-2 was built. So, the lab transferred the outdated machine to the university's campus, anticipating it to be used for research and education purposes.
The machine was managed by its Department of Electrical Engineering and Computer Science. Although MIT also owned some large computers like IBM 704, their use was strictly limited to serious research projects and ordinary students like the members of the club didn't have right to use them.
By contrast, the newly installed machine was managed under a much more open access policy. Moreover, the machine's administrator was an assistant professor named Jack Dennis, who was a former member of TMRC. So, they were allowed to use the machine unless it was used by researchers for important works. They were soon amazed by the advanced features of the machine and almost hooked on it.
Thus, those model railroad fans became probably the world's first computer geeks.
A few years later, they heard the news that an even more advanced machine, PDP-1, was coming to their campus. They were so thrilled that some of them soon began to make plans about what kinds of programs to write. Among them, Steve Russell and his friends made the most ambitious plan - they dreamed of making a video game in which you can experience a war in space.
Actually, even TX-0 had some entertaining programs like "Mouse in the Maze", "HAX" and, of course, a Tic-Tac-Toe. But they were developed only to demonstrate its high computing power and advanced features.
What the geeks of TMRC was going to do was the opposite. They used high computing power of PDP-1 to develop an entertaining program based on science fiction stories, which was their common hobby other than model railroads and computers. Especially, they loved "Lensman", a space opera fiction series written by E.E. Smith, and wanted to make a game where they can become a pilot of a spaceship.
That's why Spacewar became an innovative game. Unlike other "games" developed to demonstrate latest computers - and much similar to the case when William Higinbotham created the world's first video game, Tennis for Two - Steve Russell and his friends used the latest computer solely to entertain people including themselves.
I'll not write the details of the development history because it's so famous. Rather, I'd like to point out an important factor which enabled Spacewar to become a successful video game - MIT's open and cooperative culture.
Although it was long before the word "open-source" became commonly used by software developers, the source codes of the game were completely open to anyone. They were recorded on tapes, which were stored in drawers in their clubhouse. So, those who wanted to know its software architecture had no hurdles to access. And some of them in turn made great contributions.
It's a fact that Steve Russell constructed the basic structure of the game. But what really made the game a masterpiece were additional programs written by his friends. Without their contributions, the game would end up as just a technical demonstration of the latest machine, which in turn would delay the birth of the video game industry considering Nolan Bushnell, a co-founder of Atari, made video game his business because he saw a huge business opportunity in Spacewar.
Among them, the most important improvement was made by Dan Edwards. When he saw an early version of the game, he complained to Russell that controlling a spaceship was just boring because its movement was too linear. So, he made a suggestion to apply some gravitational effects of the sun, but Russell dismissed it by saying the machine didn't have enough power for such calculation. Edwards was so confident in his idea that he decided to write the program by himself. When it was completed, Russell saw no value in it and only reluctantly merged it with his main program.
Steve Russell (1997) :
Dan Edwards' works added nothing other than more complexity to the existed program - it didn't improve the game.Shin Denshi Rikkoku 4 (ISBN: 414080274X, p.60) NHK Publishing in Japanese,
This comment is very interesting because it shows that even the lead programmer of this incredible game didn't understand what makes a video game fun. Contrary to his understanding, the gravitational effects is the key factor of its success because it introduced the concept of "tactics" into video games.
While it's true that the gravitational effects increased the difficulty of controlling a spaceship, mastering it is an enjoyable activity; skiing and skating also require some practice before you actually experience the fun part, but millions of people enjoy them.
And it also means that your opponent can't easily predict your moves, which increases your chance to beat more skilled players by chance.
Actually, you can make absolutely unpredictable moves in the game. When you are in a desperate situation, there's a last resort function for you called "hyperspace".
It was developed by another member of the club named J. M. Graetz. By using it, your spaceship will disappear and later reappear at a randomly chosen point in the game field. Of course, there's some limits. You can only use it a few times for a single play and your situation may not get better - your spaceship may reappear in front of the opponent or a point very close to the sun, which destroys nearby spaceships.
Although those two additional features were not very well-designed, they did add some tactical depth to the game, and people loved them.
However, in the case of video games, "deep" doesn't always mean good; it's a double-edged sword. That's the key to understand why Nolan Bushnell's attempt to make money from the game failed.
Primary reference:
"Spacewar and the Birth of Digital Game Culture" on Gamasutra
https://www.gamasutra.com/view/feature/129861/down_the_hyperspatial_tube_.php