One of the major things that sets Stargate apart from many games is that it is centered around a military structure. A Stargate game is usually going to be a military experience, unless the DM goes out of their way to make it otherwise.
There are two major reasons for this. The first reason is a no-brainer: the game is based on the television show, and the show is centered on a team of (mostly) military agents sent to other planets. The second reason actually springs from the history of the gate within the game, and the reason is this: both of the stargates that have been found on Earth have been kept in military hands.
This should be a surprise to no one. The gate was first discovered and analyzed by archaeologists, but they did not keep the discovery to themselves. The gate was found to be made up of a metal found nowhere on Earth, and it seemed to have an active purpose, even if no one knew what it was at first. When scientists found a way to activate the gate and subsequently lost a man on the first trip through it, the gate was shown to be a more deadly mystery than first believed. No government would want that kind of power in unknown hands, especially with the potential it could have.
Earth had the honor of having two stargates on the planet. Most planets have only one. Both gates ended up finding their way into military hands.
A Short History
One gate was recovered in Egypt in the 1920s, as a part of an archaeological expedition on the Giza site. This gate made its way to the United States, where it was immediately placed under classified status. It was studied, used once (see the episode: The Torment of Tantalus), and then packed away. Then an investigating team of scientists - most notably Dr. Daniel Jackson - figured out how to actually control the use of the gate. (The Stargate movie deals with this discovery and the first mission through the gate.) After the mission, it was deemed too dangerous to use and was packed away again.
The television show opens up by showing the gate covered up and closed down. When it is activated from other planet, the military realizes that the function of the gate is bigger than they had first thought. Instead of only being able to go to one planet, the gate could lead to potentially billions of planets. The President and Joint Chiefs of Staff come to realize that the gate needs its own controlling force to use it, protect it, and learn from it. Thus, in 1997 they created the Stargate Command (or the SGC), which was to operate out of the Cheyenne Mountain Complex.
Although the SGC runs under the banner of the Air Force and many of its members come from the Air Force, it is its own operation. It has under its command servicepeople from every branch of the military, civilian experts from many diverse fields, and some of the best medical professionals to be found on Earth.
Another gate was recovered after the first stargate was already in operation. This secondary gate ended up in the hands of Russia for a time, and even there it was under military control. When the "original" gate was destroyed, the Russians put their gate up for grabs, but only once a deal had been struck. From the Russian military it went to the Stargate Command, which was already in full swing.
The Stargate Command
The SGC has one designated base commander who reports directly to the president and joint chiefs. The base commander is the top of the hierarchy in the Cheyanne Mountain Complex, where the SGC has its headquarters, and is responsible for much of the day to day operations of the base. The base commander not only has final authority over every off-world mission, but also has the authority to place the entire Complex on lock-down or to activate the self-destruction sequence. For most of the show the base commander has been General George Hammond, and the core book for Stargate lists him as such (although this has changed in the latest seasons of the television series). In the very back of the book they offer stats for Hammond and various levels of experience.
The core book tells us that the duty officer is the second-in-command to the base commander, but we have never seen such an officer on the television show. This is probably the case for reasons entirely related to the aims of the television show. The show has kept key SG personnel limited to a few people. Audiences come to recognize these repeating characters and come to like or dislike them more intensely because they are seen so often. Likewise, the actor who has portrayed General Hammond since the inception of the show has done an excellent job in making the General very personable and, in my opinion, irreplaceable.
The whole point of the duty officer is to put a barrier between the general SGC personnel and the base commander, who is very busy and must budget his time carefully. The television show did not want to put a barrier between the star team, SG-1, and General Hammond, and thus there has been no duty officer.
Although it is very tempting to make use of a character like General Hammond, a Dungeon Master should keep a bit of realism in mind in this one regard: very few people have direct access to the top. Most folks are filtered through the hierarchy of those in command. In a military setting, that hierarchy becomes extremely important, and going through the proper channels is pretty much the only way to get things done. The SGC does not have a bloated internal bureaucracy, however, so the average stargate team member will not have to go through as many steps to get information to the head person in charge.
That being said, it is not likely that most characters are going to start out play at Hammond's level. They are likely going to make up one of the Stargate teams. The roleplaying book lists 25 teams, and you can make more if you like. These teams have different overall functions - some are exploring teams, others are purely combat teams, while others are centered around medicine or scientific research. But the main function of each team is to brave whatever is beyond the gate, since each team is sent on missions to other worlds.
The Common Denominator: Stargate Teams
Every SG team is given a number (thus, the television show is centered around the first and most influential SG team, SG-1). Every SG team also has an internal hierarchy that is very important to consider. Many roleplaying games do not assign any sort of leadership to a group of players. If one person takes the lead and the others take orders, so be it. In Stargate, the game is designed for and with a leadership structure.
First of all, every character must have a rank. Military characters have two categories to choose from: they can be officers or enlisted. Within each category there are various ranks, from the bottom of the totem pole to the top of command. These ranks do not correspond to true, real life military ranks; the book uses its own system to simplify things.
An officer always outranks an enlisted member, and the highest ranking officer generally has command. The enlisted members also have ranks, however, so that if officers are taken out of the picture, there is always a leader to turn to. Even civilians have ranks, which determines what they get paid and what gear they can commission. There's even a feat that lets you go up a rank, if you'd like, and it can be used to try to gain control of a team.
There is one entire class, the Pointman, that is designed to lead and support a team. Just about every class ability the Pointman possesses is centered around commanding a team with greater efficiency. You can lead a team without being a Pointman, but it interesting to note that of the six base classes presented, one of them is based on how to be in charge.
The Stargate core book pretty much assumes that player characters will be set up as an SG team. This can be a great boon to roleplaying groups, and to the DM in particular. First of all, having a team helps DMs get games running pretty fast. The DM does not have to contrive a way for the players to come together or stay together. It is the team's job to work as a unit, after all, and they can get in some serious trouble if they don't. The characters will either already know of each other or will find out very quickly. Most of the characters will have some sort of background in common, especially if they have prior military experience. Also, because of military experience everyone will know how things work: orders are given, orders are carried out, or penalties will result. Even if the characters for some reason don't understand or care, the players will understand how it works since they have seen it modeled in countless movies and such.
The hierarchy of a team can be a good and a bad thing. It is good to have some sort of hierarchy when things start getting heavy. SG teams will invariably encounter violence and bloodshed, and it is good to know who will give the team orders if someone goes down. The characters are less likely to run amok when there is a voice to call for order.
The hierarchy can be a bad thing if leadership is poor, or if a player tries to take advantage of their character's position to abuse the other players. This can be avoided by a good DM who is willing to cut abuse off at the pass. If a player in charge continually makes poor decisions, the DM can give some coaching in tactics and/or find a way to replace them. If a player is being a poor sport and using their role to simply boss everyone around, the DM can use in and out of game methods to stop it. The DM can allow the other characters to mutiny. The DM can put an NPC leader in place, if necessary. The DM can also explain that even the leader of SG-1 listens to his subordinates before giving a decision.
The Stargate roleplaying game book seems to assume that you are going to start your adventures on Earth, and that things will be set up pretty much the way they are on the show: the stargate will be in the hands of the SGC, and the player characters will belong to an SG team. For DMs who have watched the show, this helps to form an idea of how things should look and act. Once you've seen a few episodes, you pretty much know how a show is going to run (at least if you're observing carefully).
Players who are familiar with the show will be able to envision the Cheyanne Mountain Complex setting easily, and they will be able to understand the massive amount of material offered in the roleplaying book with greater ease. They will have already seen the team hierarchy in action, too, since Jack O'Neill is very much in charge of SG-1. Players who are not yet familiar with the show can start playing with little difficulty, and if they choose to watch the show (which they can order almost entirely on Netflix), they will recognize many things at once.
Best of all for the DM, there doesn't have to be some extraneous reason for the player characters to adventure, or for their group to exist. The Stargate system comes complete with it's own duty, harkening back to the old prime directive of Star Trek: seek out new worlds, life and civilization in the universe. Unlike the prime directive, however, stargate teams are not ordered to stay out of the processes they find. The SGC seems to understand that by their very exploratory nature, the SG teams are bound to get involved in the destinies of other peoples.
It must be said that in many cases the life that SG teams find on other planets is not alien. Thousands of years ago, humans were herded through the gate from all over Earth, so that now human relations can be found across the galaxy. Likewise, the cultures SG teams often find are old rather than new, based on ancient cultures of Earth's past, or even on the older incarnations of alien races. The stargates themselves are not new technology but old, built by a race that is called the Ancients, and they are not called the Ancients for nothing; they were around before most races knew much about them, and they have been gone for such a long time that no one knows how to find them.