Combat System
While the combat system is not something I would of ever thought up of, it is rather cunning. In your case, cracking the west wall would take an attack over 2 hexsides (or province sides) with at least 4 infantry divisions each. You need to ensure you have commanders with fort buster modifiers and someone with an engineer capability to assist in negating the effect of the fortification. I would not attack over the river section, there is a spot further north where you can avoid the river and get your 2 hex-side attack. If the Germans have 2 divisions in that location we could expect the following combat effect.
Units in combat: The Germans get all their divisions to participate. If the French divisions are 3xinf, 1xart, 1xAA each then they can 4 divisions from 1 stack to participate and 2 from the other, for a total of 6 divisions.
Combat values : Because this is all infantry the only 2 numbers which are important is the Soft Attack and Defensivness. (Toughness is important for the attacker, but the attacker has 2 reserve divisions to replace anyone in the front line unlucky enought to run away so I will not worry about this in this example). In 1940 we could expect a Soft Attack value of 18 and a defensivness value of 32. (This actually gives you a clue why there was no casulaties in your combat - you need 3 divisions with no negative modifiers due to stacking to get any hits against a defending infantry division - which would be almost impossible if your attack was all through one hexside and suffering massive negative modifiers)
Getting Hits : To get any hits against the defending infantry division you need 3 attacking divisions. In this case the total Soft Attack value is 3x18=54. Subtract the defenders Defensivness of 32 and you end up with 22 hits against the defender. Both should get hammered the same and at 22 hits per 1 hour round those divisions will not last long. Of course once you factor in the modifiers due to fort, terrain, etc the number of hits is reduced, but even if it gets massively reduced you still have the chance of 4-5 divisions hitting a single divisions and getting hits against it. In this case the combat will last much longer, but you should still win.
Your causulaties: Your infantry divisions have a toughness of 17.7, which means the enemy has a chance of getting 2 hits per 1 hour round, per division. Considering you are dishing out up to 44 hits a 1 hour round, this is not a big issue.
I am not sure how historical this combat system is, it feels wrong in many ways - but it does work so I can't really complain too much. However some things become really obvious - the more powerful divisions will win out because it allows you to achieve the highest possible attack and defense density. (Example : If you had 3 inf brigades fighting a single infantry divisions of 3xinf brigades - the inf brigades will lose any combat. The infantry division will get a chance to attack a single brigade with all of its combat force (13.2 Soft Attack v 8.53 defensivness - ~5 hits per round). The 3 inf brigades would attack with a total of 13.2 Soft Attack - but the infantry division would have a defensivness of 25.5, which means no hits are achieved. In summary, the 3 seperate brigades are toast.
Thus, its important to get the technology which allows 5 brigades in a division. Because of the 4 x 3 frontage rule its best to keep your division frontage to 3 - but you can load 2 support brigades into your division to give it a greatly enhanced combat value. This gives you the maximum attack value through a hex-side and I assume the greatest usable defensivness in a hex/province.
