breaching
breaching is the process of entering a room and clearing all threats inside, this may sound easy but there are many things you must consider when breaching. a breach must be fast and precise, hesitating for a second could mean death.
stacking up
you stack up when your getting ready to breach, you get close the the wall beside the door; but don't touch the wall so the enemy cant hear you inside.
clearing
after you stack up, you prepare to breach. your first man covers the direct line of site of the door then checks the right side of the wall on the other side, then moves to the right corner in parallel to the door. Your second man moves in directly behind him and checks your left then scans the rest of the room and goes to the corner 90 degrees left of the door and continues to scan the room. your third man enters and stays just to the the side of the doorway on the right and scans the room. (your third man and forth man do not block the doorway) Now your forth man moves just to the left of the doorway. it should look like this.