Okay so your probably pissed at the fact that you need to pay for actual units (and also the lack of Steam cards and junk of that kind). So lets see what units you can get for free. Any info taken here can be applied to the Android & iOS version as well. 

Esta sencilla guia se concentrara en explicar como y que tiene de utilidad rescatar prisioneros en en las distintas misiones que nos presenta este juego, lo cual es bastante importante si es que se tiene la intencion de competir en igual de condiciones con... 

This guide will show you how to instantly receive everyday login bonuses and fully restore your Sortie Point Value. my first guide sorry if its sloppy. 

本指南旨在为各位零充玩家提供全成就的玩（苟）法，就是不买任何dlc完成前两个世界所有战役以及boss区域。 （另：解救俘虏虽然也有技巧（下面会提）但主要看脸。。。像我这样的脸黑玩家只能靠肝了。。。） 

It can be hard to free these fellas to unlock units and upgrades for both units AND your Base.But it will be easy if you know what do.