Blue Perks in Slot One
The Perks in Tier 1 are general utility Perks. Many of them are making their return from previous Call of Duty games. However, Sledgehammer has changed up the Pro versions somewhat, so you may be surprised at how different they can be.
Recon is unlocked as soon as you can create a class. It makes it so that explosions that damage enemies paint them on your team's minimap for a short time. Flash and Stun grenades count. This means you can toss a flash into a room, and see on your map what corner the enemy is hiding in. It lasts for 10 seconds, and even shows the enemy as a red arrow rather than a dot - letting you know what direction they're facing.
Recon Pro is unlocked by painting 120 enemies using Recon. It's benefit is that it extends to bullet damage as well, making every hit marker paint an enemy on the map for 10 seconds. This is especially useful when an enemy runs behind cover, allowing you to see what corner they're going to attempt an ambush from.
Sleight of Hand is a returning perk every Call of Duty fan should recognize. It's unlocked at class creation just like Recon. It's effect is simple: it reduces reload time by 50%. This is a huge difference for any weapon, and can be the line between life and death in a firefight. However, it can cause compulsive reloading in inexperienced players, which still leaves you vulnerable.
Sleight of Hand Pro is unlocked simply by getting a number of kills while using the Perk. Easy, right? The Pro version's effect allows you to swap weapons 50% faster. Very useful if you're running out of ammo or need to take down air support quickly.
Blind Eye is a new Perk that reminds you of Cold Blooded from previous games. It's effect is to make you invisible to enemy Air Support and Sentry guns. It does NOT, however, protect you from UAVs. It's unlocked at level 11.
To earn Blind Eye Pro, shoot down a number of enemy kill streaks - 40 to be precise. Sentry guns and SAM turrets count. Blind Eye Pro's effect is to make your launchers lock on to killstreaks much faster, and give you added bullet damage against enemy Air Support and Sentries.
Extreme Conditioning makes its return from previous Call of Duty games and it is largely unchanged. All it does is allow you to sprint for a longer duration. It is unlocked at level 22.
Extreme Conditioning Pro is unlocked by sprinting 20 miles in-game, which is easy, but time-consuming. Pro allows you to climb over objects and up ladders faster. In the end it's a useful Perk for mobility, and can allow you to chase down enemies when you're out of bullets, but given the usefulness of other Tier 1 Perks, Extreme Conditioning is the least useful.
Scavenger is the final Tier 1 Perk, and it's familiar to anyone playing the game. It's unlocked at level 39. It makes it so when a player dies, they drop a blue bag for you to pick up. Picking up those bags gives you additional ammunition. It does NOT refill your grenades, unless the enemy happens to have the same grenades or rockets you do when they died. It will, however, refill throwing knives.
Scavenger Pro is unlocked by picking up 100 resupply packs. It allows you to start each life with additional magazines and more ammo by default. Because resupplying simply requires running over the blue bags, this perk can be upgraded in a minimal amount of time.