Much as I'd like Mm and Mg to be more widely used, they're very rarely seen. TW and MWh are perfectly normal units, though.

I do find it sad that people talk about 1000 kilotons, though. It's a Tg. A ton is a megagram, a kiloton is a gigagram, and a thousand of those is a teragram. It's a pity that we don't live in a world where that's normal.