Although US forces have used Fentanyl lollipops instead of the more traditional Morphine Syrette for battlefield pain relief following serious trauma a recent scientific discovery might see morphine replaced altogether.

Instead of Morphine, which can have a range of serious side effects, scientists have been experimenting with a a pain relief compound derived from Black Mamba venom.
In the snappily titled ‘Black mamba venom peptides target acid-sensing ion channels to abolish pain’ published in the Nature Journal, the French scientists from the Institute of Molecular and Cellular Pharmacology describe;
a new class of three-finger peptides from another snake, the black mamba, is able to abolish pain through inhibition of ASICs expressed either in central or peripheral neurons
read more at the BBC
Whether this will eventually find a military application is of course uncertain, they have to be injected into the spine which makes them especially difficult to administer, but interesting nevertheless.

Into the spine means it will never have a role forward of Role 3. And there’s plenty of other analgesics in that bracket like ketamine etc etc. Cant see a use unless it does something dramatically different from the above range of drugs.
When I saw the title, my first thought was
http://en.wikipedia.org/wiki/Cobra_(anti-tank_missile)
Sorry, it was the only military “Mamba” system I’m familiar with.
What can I say. I’m destructive.