Here's a quick sampling of the various crew quality markers in the game. They range in value from "green" to "elite". The modifiers printed on the counters relate to DRMs when resolving [F] FlaK fire, [D] Diving (crash dive to elude enemy aircraft), and [A] Hit probability across All weapons.
One of the things I do with any given project is focus on mnemonics wherever possible for all game components (consider it a pet peeve of mine when it comes to try and make games more user-friendly), so this is a just a basic example of what has been incorporated in taking the game through graphic design (playtest counters had no DRM values). Ian Wedge is doing a great job with legibility (ensuring proper color contrast on counters with values). Crew quality is tracked on your U-Boat Display Mat. U-Boat crew quality is at "trained" level at game start (note the lack of modifiers).
Crew quality may increase after a series of successful patrols. Conversely, crew quality may decrease after a series of unsuccessful patrols (or crew replacement due to injury). Your crew quality can have a real impact on your patrols.