How To Beat The Enemy!

Just how tough is this game? every mission gets harder than the last. Any hints to help?

I see what the problem is. You're playing like you're in the SS, and in this timeline Hitler never came to power 

Here is a hint.
Practice 

There isnt any other general hint that covers all the missions, well maybe except for reading and understanding the mission orders.

I found there is no "cook book recipe" for winning.  The campaigns are GENERALLY set up to allow player to "graduate" from difficult to more difficult. However, I've found there are lots of exceptions to this rule.
Example, Mission three I believe for Imperial subs was tremendously hard;

took me four weeks to win that one on and off while playing other campaigns to maintain my sanity.  Certain higher missions are amazingly

easy it seems.  Skills develop with each, for example, I was not aware

of how to surface and rig for dive within 0-1 sec for awhile....this was key

to winning certain missions. 

Geeze, if there was a "silver bullet" to winning all these missions it wouldn't be too challenging would it?  We would just all DO IT and the game would be history.  Sorry, to learn and be proficient, die like the rest of us did, OVER and OVER.