RE: Stalingrad City Hexes
Firing infantry in the city is probably a waste of time - you might pick up a few kills, but the increase in low ammo, fatigue and loss of a chance to pick up replacements makes it generally not worthwhile. Their hard attack factors are just too low.
However, in a team game, commanding the 6th Army, I have managed to take the northern 3 hexes from the Soviets over the course of the first 4 days, and have almost but not quite managed to take the north and south hexes of the main Soviet bridgehead during that time frame - I might have done more but have pulled most of the panzers out of the city and sent them west.
I did it by:
Firing artillery, even though the losses are not heavy, any losses will build fatigue which is critical. Nebelwerfers are best though and should be concentrated.
I did fire full strength infantry, especially the panzergrenadiers, against my targets, but I rested ones with losses/fatigue. This rarely caused losses but see above.
Move up all available 88s adjacent to the target hexes. They will get consistent kills - I used my other ground units to draw off some defensive fire when doing this, but I still lost a few guns in moving adjacent to the Soviets.
The German tanks with higher HA are good also, although vulnerable to Soviet fire in return.
Once I started causing some damage to the defenders of a hex, I would launch assaults to finish wearing them down, even though not all defenders were disrupted - otherwise, they seemed to recover from disruption quicker than I could get the last unit or two disrupted by fire.
PATIENCE is required. I took the first hex sometime on the second day, the second around the end of the second and third maybe early on the 4th? It requires time to wear them down through losses and fatigue, and luck to disrupt the defenders.
There are also a couple of hexes that are towns rather than cities, they are more vulnerable to fire, and Soviet HQs have a slightly lower defense value and so are easier to disrupt and then make the recovery from disruption of the other units assigned to its command less likely.
Finally, the Soviets sent reinforcements into my target hexes, but they land in travel mode. Set your infantry to destroy them if possible - they can kill huge numbers and greatly weaken these new units - you don't want them stronger and recovering from disruption, making it that much harder to clear the hex. I managed to kill 90% of the manpower in the few units that landed, give or take.
Good luck with it.