3 C4 with explosive spec to take out a building iirc. just had to place them properly to take out enough panels.
It was still six, wasn't it? 2 on the "middle" foundation that ran across the first floor. Four in the corners. If not that maybe one or two less if you put a C4 under the "corner" landing of the stairs to blow the "four corners" and the foundation to trigger the collapse.
D2.0 on objectives wasn't so good, but objective damage, especially after they doubled it, was great. meant you really had to work at it to actually destroy it.
Objective Damage was always meant to be a side-goal and had good intentions, sure. But when the majority of rounds were played where people were rocket/tank-sniping and
going no where near the objective because hey, why waste tickets to play the mode? It was a bad thing. Raising the "damage-to-kill time" didn't really solve the issue. It just showed the issue was a problem that DICE didn't intend for it to be.
You could Rocket Snipe/AT4 and Tank Snipe about 80-90% of the crates in Bad Company 2 Rush depending on your position and how good you were with the AT4 (given the projectile would disappear after a certain distance so you had to pre-cog it trajectory with the box and know where it was in relative space 24/7). Adding a few more rockets just meant you had to waste maybe one or two more tickets depending on how good your aim was and depending on if the defense was a complete dunce to not at least attempt to stop you.
The only two you couldn't was redesigned A last set White Pass (after it was a <D 2.0>) and Last set B (since it was behind indestructible cover, oh hey Dream!) Nelson Bay.
Edit2: But let's be fair: When the maps could be made to look like the surface of the moon and to where people couldn't push up because they ran into no-man lands (oh hey, BF4 design!) where the defense could see them coming because of the linear map design + destructible trees? I can't blame the attackers for being forced to go that route.
Edit: And actually thinking on it. Set 2
wasn't fully a complete tank-snipe on Arica. B could be taken via <D 2.0> with the tank (or a UAV!) collapsing the building but the tank can't hit the bleed-through wall or Roof of A. It could if it pushed up into the "town" but not from afar.
Set 3, meanwhile. A could be tank sniped (despite the indestructible bus supposed to prevent that) and B on the train car could. Set four (further down the train line) could as well depending on player position (and could AT4 snipe B in the building if you were good with the AT4 at long distances, I guess).
Last set/5 was the one where all that stopped because they added a few indestructible panels in the construction area for A/B. IIRC.