Trainees: 1-6
Time: 10 minutes.
Trainee Difficulty: Medium
Trainer Difficulty: Medium
Required Location: The MOUT training area
Recommended Prerequisites: None

To teach trainees how to minimize the risk of entering an enclosed space, such as a courtyard or room, that potentially has enemy defenders inside. It teaches stacking techniques as well as a good entry procedure.

1. Briefly explain that stacking is when soldiers line up on either or both sides of a narrow entrance before breaching to maximise fluid and fast entry (if necessary).
2. First tell the trainees about the two types of stacks and when to use them
   1. Side stacking means that soldiers stack on one side or the other. Generally used when the entrance is not closed or covered (and arch in a wall or an open door). The advantage is that it does not require the soldier to move into a space where he can be seen by people inside the area to be breached. The disadvantage is that it can be a slower method of entry.
   2. Split stacking is where soldiers line up on either side of the door. It is only recommended that this be done if the door is closed and opens inwards to avoid exposing anyone to defenders on the inside. The advantage of this is is that is can facilitate a faster and more fluid breach. The disadvantage is that is can only be done safely in a few situations.
3. The explain to the trainees that when entering the room the first and most important consideration should be minimising the time that the team spends in the so called “fatal funnel” whilst getting the most guns into the room. The “fatal funnel” is the area in and and immediately inside and outside the doorway. Any human players inside will be focusing on this area if they're expecting a breach
4. You may wish to note that it's less of an issue against AI but their rapid reactions and excellent aim as well as complete lack of panic make this a moot point.
5. Next it is important to get as many guns into the room as possible. This means that trainees have to unlearn the instinct to stop in the doorway upon spotting enemies inside the room. They need to keep moving so as not to block friendlies from coming to their aid against said enemies.
6. Mention that before briefing their weapons should be set to burst or full auto and they should have a full magazine.
7. Explain the difference between “hooking” and “crossing”.
   1. “Hooking” is when a soldier enters the door and immediately turns back in the direction they entered from, making a hook like trajectory when seen from above.
   2. “Crossing” is when they continue to move in the direction they entered in to the opposite corner.
   3. Explain that there's no firm guide as to which method is correct. It's a judgement call that the point has to take.
8. Explain how to move through the door
   1. The team leader may give instructions on whether the pointman should hook or cross. If he does not, the pointman can choose what to do on his own initiative.
   2. The point man enters using whatever movement method was chosen and keeps moving into the room, moving out of the “fatal funnel” and engaging targets of opportunity.
   3. The second man in the stack then moves into the room using the opposite method of movement. So if the pointman hooked, he crosses and vice versa. He also moves out of the “fatal funnel” and engages targets of opportunity.
   4. The rest of the team follows, alternating movement methods as they go.
   5. Ideally, they should try to space out as much as possible and not clump up together.

• This exercise is effective with human opponents and AI opponents and both should be used if possible as both types will be face in missions.
• Grenades can also be used but only with caution.
  • Flashbangs don't work on AI
  • Frag grenades' shrapnel can potentially penetrate the wall you're stacked against.
  • ARMA physics. Your grenade may not go where you mean for it to go. Everyone will blame you if it doesn't.
• Team leaders should carefully judge how many soldiers to send into clear an area. A fireteam is about the largest element that should ever be sent into a building. Any more than that and they're get in each others way. If there's an ambush you may lose everyone you sent in regardless of size. More soldiers means more chances of accidental friendly fire from mistaken identity, ricochet or penetration.

As usual, Dslyecxi's TTP3 is an excellent resource and has a section on stacking and room entry.