How to get the Secret Elite Mercenary Achievement/Trophy for Contra: Rogue Corps

How to get the Secret Elite Mercenary Achievement/Trophy

The Elite Mercenary is a secret achievement/trophy and by far the most difficult one to get in the game as you need to ge an S-Rank on all the main missions (this does not include the exploration missions). In order to get an S-Rank certain requirements must be met, you must complete the mission with at least 10 minutes left on the clock, get a high number of kills, and collect around 75% of the golden cannisters. Meeting two of these three requirements should be enough to get the overall S-Rank.