How do I get S+ or better soldiers?

There are four ways to get S++ staff

1. Events: every maintenance period (every two weeks or so), you can play the quick event FOB missions and exchange the points for S++ staff. You're limited to a single exchange of 3 S++ staff for each skill (you can also get a shit ton S+ guys this way)

2. PF Points: Similar to the Event FOB missions, you can earn points through your automatic PF battles and exchange for S++ staff

3. FOB Missions: When you successfully infiltrate any rival's FOB, you automatically capture 10 staff members whose skill is based on the platform you're on. Pay attention to the grid that shows the rival staff's rank just before spawning in. Remember that the maximum number is 500 staff members on any given department. Therefore, if a certain platform shows that they have 432 S+ and 68 S++ assigned, that means the 10 guys that you automatically capture from the successful infiltration will be AT LEAST S+. I once infiltrated an FOB that had MOSTLY S++ assigned inside. 8/10 of the guys automatically captured were S++. Remember also that these 10-captured guys go into your FOB brig until your rival's wormhole dissipates. There's some FOB's that have S+/S++ staff patrolling the decks, themselves, which is really handy if you're looking for combat staff. These guys go in the same FOB brig. Successful infiltrations will also earn you 10 volunteers, whose rank can sometimes be up to S++ if the FOB level was high enough. These guys will go straight into your staff (and not the brig) since they're volunteers

4. Hack.