At the end of each mission in Commandos: Behind Enemy Lines, merit is awarded, and the player may be promoted for excellent performance. Enough promotions are supposed to grant access to a secret mission.
The game manual says that merit is mostly awarded for time taken and damage sustained, and that enemy casualties are irrelevant. It does not confirm nor deny that those are the only factors however. The mission completion screen looks like this:
Merit has zero stars because it's like an experience bar, when maxed it goes to the next level. Most of my missions look exactly like this, but without the promotion message and with 3 stars lighted up for merit, indicating only half the maximum amount gained.
I have been doing the missions and achieving some amazing speeds by having all characters doing different things at the same time, and my "time" meter is always full. However, this rarely results in a promotion, and I always restart the mission until it does. Are there other factors that affect merit gained and are not reflected in the end screen? Which? Is it all about time, with the end screen giving three stars for speeds that are good but not enough to rank up, and the same three stars for truly awesome haste?