The medical team is unlocked at the same time as the main quests progress to the point where you can build the FOB.
Missions to unlock:
Mission 32: To Know Too Much.
Mission 38: Extraordinary.
Mission 41: Proxy War Without End.
Mission 43: Shining Light. Mission 43: Shining Lights, Even In Death.
Mission 45: A Quiet Exit.
Mission 46: Truth: The Man Who Sold the World.
Branch - Get the AI Pod. Extract the AI Pod.
Branch - Secure the Remains of the Man on Fire.
Branch - Search for the Escaped Children 1.
Branch - Search for the Escaped Children 2. Search for the Escaped Children 2.
Branch - Search for the Escaped Children 3 Search for the Escaped Children 3.
Branch - Search for the Escaped Children 4 Search for the Escaped Children 4.
Search for the Escaped Children 5.
Branch - Search for the Escaped Children 5.
Branch - Save Secure Quiet.
Useful Tips:
1. The arrow keys plus two hits of R2 will drop you, not pick you up.
2. When you're holding someone, you can use the trajectory keys to use the enemy as a shield.
3. If you stand behind an enemy and raise your gun, the enemy will put it down and surrender.
4. Every time you get close to an enemy, you'll be spotted because you're wearing the wrong costume. Wearing a sneaking costume eliminates the sound of footsteps, so you won't have a problem walking any way.
5. Upgrade the balloon before you can start grabbing carriers and cargo containers.
6, the sniper partner is overpowered, please bring more out of the mission, wait until there is a cover fire command, really makes the level super simple.
7. You can get high ratings for killing people. If you're fast enough and don't exaggerate, you'll get an A or higher.
8. When you're spotted by an enemy, you don't count as being spotted if you make the enemy invulnerable during the slow-motion period. It also doesn't count as triggering an alarm.
9. By blowing up the radar truck at a stronghold, you can designate a helicopter to fly to that stronghold.
10, blowing up the enemy's communications equipment will repair it some time later.
11, there will be multiple mini-quests within a mission, even if you don't do them all, you can still get an S rating.