[HiTech RedNeck]

How would toting a tiny nuke to a bridge, etc. be quicker than shooting a missile?

[Tree of Liberty]

I'd think it'd be dependent on the ordnance and manpower available and the energy required to take out the piece of infrastructure in question. I imagine that it'd be for LARGE bridges similar to the Golden Gate or Brooklyn Bridge in size, or caverns and caves like Iwo Jima. You'd have to talk to a military engineer to get specifics. I'm just going speculating based on things I've read here and there.