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:

1. The US Navy SEALs is arguably the top special operations force. Created in 1962, the Sea-Air-Land operators go through years of training and, especially after 9/11, endure an incredible operation tempo. Many foreign militaries base their special ops on the SEALs.

2. The UK equivalent of the Navy SEALs is the Special Boat Service. The selection process involves a grueling endurance test, jungle training in the rain forests of Belize, and combat survival training, which involves intense interrogation of candidates. And you get only two attempts to pass.

3. The British Special Air Service, known as the SAS, is the infantry counterpart to the Special Boat Service. Their insignia bears the phrase "Who dares wins." Asked about the importance of the SAS's role in the fighting that followed the Iraq War, US Gen. Stanley McChrystal said: "Essential. Could not have done it without them."

4. Israel's Sayeret Matkal is another of the world's most elite units. Its primary purpose is intelligence gathering, and it often operates deep behind enemy lines. During the selection camp (Gibbush), would-be recruits endure hardcore training exercises while being constantly monitored by doctors and psychologists. Only the strongest get in.

5. Few of the world's counterterrorism forces can compete with France's National Gendarmerie Intervention Group, or GIGN. The group is 200 strong and trained specifically to respond to hostage situations. It claims to have freed more than 600 people since it was formed in 1973. It is against the law in France to publish pictures of its members' faces.

6. Russia's Alpha Group is one of the best-known special forces units in the world. This elite antiterrorism unit was created by the KGB in 1974 and remains in service under its modern-day counterpart, the FSB.

7. Spain's Unidad de Operaciones Especiales — or the Naval Special Warfare Force, as it has been known since 2009 — has long been one of Europe's most-respected special forces. Established as the volunteer Amphibious Climbing Company unit in 1952, it has since become an elite fighting force.

8. The Special Services Group in Pakistan is better known in the country as the Black Storks because of the commandos' unique headgear. Training reportedly includes a 36-mile march in 12 hours and a 5-mile run in 50 minutes in full gear.