1. Open folder: Swat 4\Content\System
2. Open file: "Swat4.ini"
3. Press Ctrl+F, then search for "ReduceMouseLag" key
4. Replace: "True" to "False"

Then, in same folder 2. Open file: "User.ini" 3. Left click before any "[", hit Enter twice then hit arrow up twice 4. Add the following lines: [Engine.PlayerInput] bInvertMouse=False MouseSmoothingMode=0 MouseSmoothingStrength=0.000000 MouseSensitivity=1.00000 MouseSamplingTime=0.001 MouseAccelThreshold=0.000000 DoubleClickTime=0.200000

Taken from: https://www.gog.com/forum/swat_series/low_mouse_speeds_when_start_of_mission_on_swat4_help_please/post4