There are endless crowds of enemies in The Division, and they're going to be pouring bullets into your crew from dawn until dusk. If you want to play as a Tank-type and draw their fire away from your friends while avoiding being killed yourself, here's the best way to do it.
Ballistic Shield with the Kinetic Breaker mod
The shield, which you'll find in the Security tree, has a huge drawback: it limits your offense to sidearms only while you've got it out. However, for the tank, you're not there to slaughter the enemy single-handedly but to draw their attention, and having the ballistic shield out draws aggro to ensure the enemy focuses on you. The Kinetic Breaker mod means your shield converts a percentage of incoming damage into health, so you'll be able to recover from wounds while receiving them.
Turret with the Active Sensor mod
You don't need to Tank alone: bring a little friend, the turret. It's not a major damage dealer, but neither are you—the real idea is to attract attention and draw enemy focus. The turret can be placed or thrown, and will open fire on nearby enemies. Best of all, it freaks them out and they'll shoot at it rather than at your teammates. The Active Sensor mod will pulse the enemies it hits, making them visible to the damage dealers on your team, especially useful if no one has equipped the Pulse skill itself. I prefer Active Sensor to Dragonbreath, which turns the turret into a flamethrower, because while setting enemies on fire is fun it also makes them a bit difficult to see.
Signature Skill: Survivor Link
As with the medic, you'll want to save up your Security points (1,000 of them) to unlock the Barracks and receive the signature skill. When activated it speeds up your movement rate and increases your damage resistance, and being mobile and durable is important to any Tank. Teammates within the radius get these buffs as well.
Not all of the Tank's talents come from the Security tree. Strike Back, from the medical tree, is useful because when you reach low health it reduces the cooldown time of your skills, meaning your shield and turret will get back up and running more quickly. I recommend On the Move from the Security tree, which reduces incoming damage by 30% for 10 seconds if you kill an enemy while moving. Repo Reaper awards you with a mag for your primary weapon when you kill an enemy with your sidearm, which you'll definitely be doing while using your shield.
Key Stat: Stamina
You probably could have guessed. Being point man means drawing aggro and absorbing damage, so beef up your health with stamina-enhanced gear. You'll want to minor in electronics as well, though. Your skill-based gadgets are going to be taking a lot of punishment, and having gear with healthy electronics attributes means they'll be more durable, just like you.