Are Marines/Mountain troops worth it?

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If there is any chance of enemy opposition, Marines are a no-brainer. They are worth every IC. Also useful in swamps, over rivers and in jungle.

Mountainers are so-so. In HoI2 they were nice since they had winter combat bonuses, but in HoI3 I usually don't use them. They have not enough firerpower, so their hill/mountain bonuses make them not strong enough to justify the cost.

 

[GAGA Extrem]

Does adding support brigades to special forces mess up everything?

I suppose that for Marines, the Artillery would just function as in any other division, but for Mountaineers it would affect their movement. Right?

The problem with adding brigades is that the average combat modifiers are calculated as a mean value among all units.

Let's do the math, shall we?
We got:
MAR with 2.5 SA and a 50% shore attack bonus
ART with 4 SA and a -80% shore attack penalty

A DIV consisting of MAR-MAR-MAR-MAR will have 10 SA and a +50% bonus, thus it has 15 effective SA.

A DIV consisting of MAR-MAR-MAR-ART will have 11.5 SA, but will only get ((50+50+50-80)/4 =) 17.5% shore attack bonus - thus despite higher base attack, you will only have ~13 effective SA.

A div consisting of MAR-MAR-ART-ART will have 13 SA, but will also get a ((50+50-80-80)/4 =) -15% shore attack penalty, thus it has only ~11 effective SA.


So adding brigades to special units increases their overall combat value, but decreases their usefulness within their special role. Although it can be cheaper to just add some ART brigades to fill the DIV slots, I usually tend to make "pure" units.