The 81st hosts strat runs as often as we can. From what we can tell (based on the help site description) if you knock the industrial center down to 0% it's supposed to take 3 hours for it to rebuild. If you knock the training facility down to 0% it would take 3 hours but it requires the city to rebuild. So if you hit city, then training, you can effectively knock out troops for 6 hours. The most damage we've been able to do is knock the city down to 4%. My question is the flak towers in the city, are they considered part of it? It takes 20,500 pounds to drop the city (by specs, using 84x250 pounders, we always use 500's) but if you throw the flak towers into it (just the 2 in the industrial center itself) that numbers jumps to 92,500 pounds.