How do I use the hellbomb?

Just unlocked the hellbomb on the PC. How do I use it effectively? So far, it hasn't destroyed anything at all, and only succeeds in killing me and my friends. Big tanks? Structures? It doesn't make a dent!

For starters, how do you drop it? I've heard you can, but after three missions with it, I haven't been able to find the correct key. The control menu wasn't much help either. Getting sick and tired of blowing up to little to no effect.