Elite special forces are some of the best-trained and most formidable units a country can boast.

They go where other troops fear to tread, scoping out potential threats, taking out strategic targets, and conducting daring rescue missions.

These are the best of the best.

Though it's extremely difficult to rank these forces relative to one another, some units that rise above the rest with their track records and the fear they instill in their adversaries.

These troops have been through rigorous training exercises designed to weed out those who can't hit their exacting standards.

In a world in which the sheer size of a country's military is no longer the only guide to its effectiveness, these troops are the ones that states look to to get the job done.

Note that there are some graphic images below that some readers may find disturbing.

Tomas Hirst contributed to a previous version of this post.