S.S.D.D.

S.S.D.D is the first level in Call of Duty: Modern Warfare 2. It serves as a tutorial to teach players basic gameplay mechanics.

Walkthrough
The level starts with PFC. Joseph Allen and Sgt. Foley training some troops who can't fire accurately. Sgt Foley tells Allen to do a quick weapons demonstration. Allen picks up a M4A1 and shoots the targets and then tosses some frag grenades. After teaching the militia, Foley tells Allen to meet Cpl. Dunn at The Pit. Dunn demonstrates that switching to your sidearm is faster than reloading. Then Dunn tells you to run the course. In the course, you have to clear enemy emplacements and then clearing out a building without civilian casualties. After running The Pit, you choose the difficulty. Shortly after leaving The Pit, an alarm sounds and soldiers will rush to a group of returning group Humvees that have brought wounded soldiers from BCT One. Sgt Foley yells to the squad to ready up, and you then prepare for battle. Also at the end of the Pit, you can hear some Rangers talking about Soap's, Roach's, and Ghost's obstacle course scores.

Trivia

 * S.S.D.D means "Same Shit, Different Day", derived from Stephen King's book, "Dreamcatcher". This goes along the lines of F.N.G., meaning "Fucking New Guy", in Call of Duty 4: Modern Warfare.
 * One of the spectators in the Pit is a man by the name of Cpl. Bowling. This is a reference to Infinity Ward's Robert Bowling. (The same soldier can be found in the level In their Own Accord)
 * U.S. Rangers can be seen playing basket ball, repairing a military hummer, on guard towers, exercising, looking at a phone, and eating chocolate. If the player gets close enough, they can hear their conversations.
 * One of the conversations is about a group of "Delta" soldiers who came though the base recently - they are actually talking about Soap, Ghost, and the rest of Task Force 141.
 * Notice that the Afghan militia soldiers wear the 6-color "chocolate chip" desert camouflage used by U.S. troops during Operation Desert Storm.
 * The Special Ops level of the same name is the exact remake of The Pit. Topping it off with Shepherd "encouraging" the player.
 * Notice that Joseph Allen is a Private First Class and most of the locals "who spray the bullets all over the place" have higher ranking than Allen himself.
 * After running The Pit once, the player will find more weapons.
 * The target upstairs which the player must melee will already be popped out in Special Ops. In Special Ops that target cannot be shot.
 * After completing Sgt. Foley's shooting test press the frag grenade button and a message will appear that says "No M2 Frag Grenades Remaining.". This is incorrect: the M67 (not the M2) is the primary Fragmentation Grenade used by the U.S. military and used in the game itself.
 * When going to the Pit, walk along the fence, and notice a guy eating a chocolate bar. Afterwards, walk a little further down and notice a fully dressed Ranger loading his M4 magazines with rounds from a box that says ".50 Caliber" on the side. This is incorrect as the M16/M4 use the 5.56x45mm NATO rifle shell.
 * Try to shoot one round at a time to maximize accuracy and minimize ammunition consumption.
 * Choosing the difficulty after running the Pit will make the player "complete" the whole level in that difficulty. Therefore they can't choose the difficulty when they start the level.
 * If the player stays at the firing range Sgt. Foley will continue to show the locals how to fire their weapons.
 * A lone Mark 19 Mod 3 automatic grenade launcher can be seen on a tripod on the ground next to one of the Humvees, but this weapon is never used in-game.
 * The intel piece in this level is the easiest to acquire in the game, it is located next to a guard tower.
 * Strangely, at the end of the level, when the wounded men arrive, none of the doors of the hummers are open.
 * It is recommended to use an MP5k and the USP .45 combination so that the player can move faster while aiming down sights, and to take out the targets more quickly if the player has to reload.
 * When Foley is training the locals, he is not speaking to them directly, there is a translator next to him speaking to the locals in Dari.
 * Sometimes a soldier will say "Private, have you ever seen a grown man naked?" This is another reference to the movie Airplane!.
 * In one of the conversations, a soldier is talking to a Lieutenant about an assault bridge; however, there's no Lieutenant to be found in the level.
 * If the player chooses Veteran difficulty after the Pit, then they will be asked to confirm their choice three times.