Machine guns are best used with the army, providing valuable suppression of charging enemy infantry and also being protected by your front line troops. Leaving them on their own risks them being flanked and killed, taken out by vehicles OR losing a fight on the front lines because you have a machine gun defending the flank.
Let's take a look at an example.
Here, you can see that the German team (in gray) is defending two points on the map. Their MG is setup to the east in a building, preventing approach from that direction. Their two grenadier squads are defending the point to the left. A hedge blocks line of sight and movement between them. This is based on the northern area in Kholodny, by the way.
The Russians are attacking the west point using a large group of infantry. They will easily overwhelm the two squads there (forcing a retreat) and end up taking the point. Then, they will likely follow up on the supported MG42 and toss grenades or Molotovs in, also forcing a retreat or possibly even a kill on the machine gun.
Here, you'll note that the German player kept his entire army together to the west. The Russians attack, and it's an easy German win with the support of the machine gun.
Potentially the Russians could have attacked to the east and the Germans wouldn't have been in position, but at least they could turn and fight together as a group instead of being defeated piecemeal.
Key points of this tip:
- Keep your machine guns with your army (but in the back)
- Don't leave machine guns deployed in a building or to cover a route if your main army isn't strong enough to beat theirs head on
- It's better to fight a battle with your whole army on even ground than it is to fight with part of your army on favorable ground
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