‘Three Man Army’ is a Bronze Trophy and 20G achievement in Grand Theft Auto V which requires you to Survive 3 minutes on at least a 3 star Wanted Level with all three characters together off mission.
Before I get into this; note that not all the endings in the game allow you to obtain this Achievement/Trophy after the story is completed. Anyway, to earn this; you must have unlocked Trevor in the story mode. Once you have all the three characters; you can call them and arrange a meeting.
GTA 5 Three Man Army
Anyway, make sure you equip yourself and your car with toughest armor so as to sustain the continuous fires from police officers. Another thing you will need to complete it is a vehicle having 4-passengers capacity.
Get a suitable vehicle and call your Michael and Trevor to meet up with them. They will appear on your mini-map. Quickly get to them and pick them up.
You can then shoot some civilians and armed officers to attain a three-star level. Alternatively, you can get into a military base or Los Santos International Airport to attain these stars much quicker.
Once you have attained the police attention; all you need to do is to roam around the city or the airport for three minutes and the Achievement/Trophy will pop-up. If you think, you are losing the sight of the cops; get into their search cone and the pursuit will continue.
Note: You might have to honk your horns to get the attention of Michael and Trevor. Also make sure that you pick the other two characters quickly or they will disappear from the place and will not receive your phone calls.
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