Day One was one of the few maps to be mentioned prior to the release of Gears of War 2. This map appears to be shaped in the style of a cross. It also has a similar design to the previous map Raven Down. The map is also the tutorial map in versus mode. The only difference is the new weapons, new geometry deco, and the balconies on both sides. If you look inside of the arcade section of the map, you will locate a Boom Shield, which can be useful whilst playing games of Annex, due to the fact that the Boom Shield can be deployed as cover. Also, if you go up the balcony in the arcade section, you will find a cycled weapon between the Longshot Sniper Rifle, and the Torque Bow. Directly opposite is another building also having a balcony. Atop that balcony, you will locate a cycled weapon between the Hammer of Dawn and the Mortar. There are two buildings without balconies, inside of them are the cycled Boltok Pistol and Gorgon Burst Pistol. In the middle of the map is an Emergence Hole, which is the size of a Seeder. Interestingly, during multiplayer matches (Game types exclude Horde), a Seeder will randomly rise from the Emergence Hole, but it does no damage and cannot be killed, and sinks below again after a few seconds. Day One is also the map that the five training sessions take place on.
This might work for you if you're good with a Gnasher Shotgun. You and the rest of your team should pull out your Gnashers and circle the map around the Emergence Hole. Take turns grabbing ammo where it appears. Don't worry about larger enemies, they shouldn't be a problem if you all focus your fire on them. The only thing you really need to worry about are Cyclops and their Lancers. This has been tested to Normal.
Another strategy is to use the staircase and balcony on the right upper corner of the map. This area is marked by the huge REGENCY sign. The team can block the bottom of the staircase with a Boom Shield, which will hold back Bloodmounts and Maulers while using the re-spawning Hammer of Dawn or Mortar to kill the other Drones, Snipers, Boomers, etc. who take cover behind the scattered debris and vehicles. The only downside to this is that the area is pretty open, and hell can occur if an unnoticed Boomer or Grinder gets to the staircase. Also, if the shield happens to fail, the entire team is trapped. However, if this does occur, a last resort is to retreat back around the corner of the balcony and go over the air conditioning vents. Bloodmounts and Maulers cannot enter this small area, but there is no cover on the player's right side. Another advantage is that an ammo box is located close to the stairway, and the pistol respawn point is not much further. This is helpful so that the team can replenish their ammo between waves or in short breaks in the battle.
If you feel cramped in this small area, split the team and have two players make their way to the other side of the map and hold up in the balcony over the casino/arcade. This area has less cover than the REGENCY balcony, but has a better fall back area which is boxed in by air conditioning vents, located in much the same fashion as the other balcony. Of course, this comes with the pros and cons of defending two areas, such as securing another Boom Shield and fighting with a less concentrated force. However, this causes many enemies to get caught in the cross fire between the two points, making them less likely to successfully find cover from the storm of bullets, and not to mention the Mortar rounds and occasional Hammer of Dawn blast. It also provides a backup plan in case one side is overrun by Locust forces.
- Day One is suspected to be set on E-Day because the structures are new and undamaged, and the name of the map also suggests it. Plus, in the beginning cut scene of Gears of War 2, the Locust emerge there on Emergence Day while they attack civilians.
- The arcade machines have comedic names. Also, they have the Skee Ball game and foosball-like game of Thrashball.
- Day One might be a spiritual successor for Raven Down, as both are built as a cross, with an inaccessible center, and inwards corners of the cross have interiors.
- The Seeder that pops out of the Emergence Hole never fully disappears after it pops out. This can be proven by shooting the tip of its leg when it is inside the hole as blood can be seen spurting out.
- The Thrashball table game will play random lines from Augustus Cole every now and then. The most often occurring lines are "Wooh!", "Bring it on!", and "Ain't enough freaks to stop this man!".
- Players spawn on the "top" and "bottom" of the cross, always facing each other. However, AI's in Horde mode spawn throughout the entire map, inside the arcade, and on all four points of the cross.
- The Down But Not Out Cafe, Regency Theater, Pawn Mart, the Selkirk Hotel, The Family Fun Arcade, and Sera News are located in this map.