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Fourth episode of 'Time To Kill', a series devoted to the inner workings and mechanics of Call of Duty's multiplayer.

Episode four focuses on mobility - an essential part of traversing the battlefield, and part of establishing a positional advantage.

Positioning is key in Modern Warfare 3 - whether aggressively rushing or playing with a more conservative approach, your location will do much to determine your success.
In this episode, we're covering mobility.

Your base movement speed is determined by the weapon you carry - heavier weapons will slow you down, whereas others will let you move unhindered.
SMGs and Shotguns are the fastest weapons available - when using these you'll move at maximum speed, prior to any modifiers.
Assault Rifles and some of the Sniper Rifles - the L118A, the MSR and Dragunov, grant intermediate mobility - at 0.9x movement speed, a 10 percent penalty when compared to the fastest weapons.
The LMGs, Riot Shield, and remainder of the sniper rifle category - the Barrett, RSASS and AS50 - are the slowest weapons available, each decreasing your movement speed to 0.8x the maximum, a 20 percent penalty overall.
Secondary weapons adopt the movement speed of your primary, so switching to a pistol while using an LMG will not grant a boost to your mobility, like it did in Black Ops.
However, picking up two secondary weapons will grant you maximum mobility.

If you're using the Overkill perk, your base movement speed will be that of the slowest weapon you carry - so an SMG paired with a Shotgun will retain 100% mobility, while carrying an LMG with a Riot Shield will not reduce your base movement speed below 80%.

Your stance also affects your movement speed - standing up is the fastest means of getting about, with no penalty to your movement.
Crouching will slow you down to 65% of your base movement speed, and going prone will reduce your speed further - to a mere 15% of your base speed, a snail's pace.
Moving laterally will also slow you down, at least slightly - while moving forwards you'll travel at full speed, but when strafing or reversing you'll move at 97.5 percent of your maximum speed.
Aiming down your sights also imposes a movement penalty - the degree of which depends on your weapon class.
SMGs, Machine Pistols, and Handguns will allow you to move at 0.8x base speed while aiming - this will stack with other penalties, so for example moving while aiming and crouching with an SMG will result in mobility a little over half your base movement speed.
Assault Rifles, LMGs, Shotguns, Snipers and Launchers will move more slowly whilst aimed - with a 0.4x multiplier.
Should you employ Stalker in your third perk slot, however - the penalty for aiming is completely removed, allowing travel at your normal rate while aiming down your sights - particularly useful with these slower weapons.

The LMGs, Sniper Rifles and Riot Shield all have a 'Speed' proficiency available, which will affect your movement speed with that weapon.
The proficiency acts as a straightforward 1.1x multiplier - so the LMGs, Riot Shield and slow Sniper Rifles will move at 88% of maximum speed, and the Fast Sniper rifles will move at 99% speed - almost as fast as an SMG or shotgun.
The speed bonus only applies to the weapon in question though, so you lose the 1.1x multiplier should you switch to your secondary, or replace your primary with another weapon.
When using the specialist strike package you will gain the speed proficiency when you reach 8 kills (or 7 with hardline).
This applies even to weapons that normally wouldn't have the option of increased movement speed - but does not apply to a weapon that already has the speed proficiency active.

Finally, the Juiced deathstreak will apply a temporary multiplier to your movement speed, granting 1.25x your base speed for 10 seconds.

Another major component of your mobility is sprinting - sprinting sacrifices your ability to fire your weapon for increased movement speed, allowing aggressive players to reach critical objectives first and to surprise slower opponents.
Sprinting will increase your movement speed by 50 percent - allowing you to cover more distance in a shorter timespan. However, your ability to sprint is limited by your stamina.
Your sprint endurance is around 4 seconds by default, permitting faster movement for that length of time only.
After expending this sprint endurance, you can walk normally - but won't be able to sprint again for a couple of seconds, and won't regain full endurance until some time after that.
You can increase your sprint duration with the use of Extreme Conditioning in your first perk slot - this will double your available sprint time to around 8 seconds, allowing for positional advantages and earlier intervention at objectives.