Here you have a delicious suggestion in case you are currently playing Metal Gear Solid V: The Phantom Pain, and we know you are. This tip regards the legendary gunsmiths, since we highly recommend you to get them to your Mother Base as you as you can. They are three and each of them has a particular reason why you should extract them. Also consider they are really easy to extract.
The first is an A Rank.
The second lets you customize camos on your vehicles.
The third (and the best) lets you customize and add extra attachments not available elsewhere to your weapons.
The side ops where you unlock them is available right after main story mission 13 (the first in Africa). However, it may not unlock right away depending on what other side-op you have available. The maps for both Afghanistan and Africa have regions that divide them up. Each region has multiple side-ops in them, but only one side-op at a time will ever be available to start.
This is determined by an internal mission priority. Highest priority op is shown, and the next one will be available only after that first one is completed. For example, Legendary Gunsmith is located in the North-West region of Africa, but so is another which was to find a Motherbase soldier. Mother Base Soldier op has higher priority.