The Navy's SEALs (Sea, Air and Land) teams have the reputation of having the toughest military training of any group in the world, with a dropout rate of 80 percent. As the name makes clear, they're trained specifically to be badass in any environment where they're needed.
2. SEAL Team Six
Operation Neptune Spear -- aka the assault on Osama bin Laden's compound in Pakistan -- thrust ST6 into the public consciousness for the first time. Made up of recruits from the SEALs and the Navy's Explosive Ordnance Disposal units, they are a highly elite and almost entirely secret unit. In other words, the best of the best.
3. Delta Force
Just about the most elite of the elite, Delta Force is a Tier One counter-terrorism and Special Mission Unit, and as such much of the information about them is classified -- their operators don't even wear military clothing while on duty to make them anonymous. They were created in the 1970s specifically to deal with the growing threat of terrorism.
4. Green Berets
The official name of the Green Berets is the United States Army Special Forces. To give you a sense of how badass they are, here's their job description: unconventional warfare, foreign internal defense, special reconnaissance, direct action, hostage rescue, and counter-terrorism. Makes your day job seem pretty weak by comparison, right?
Kept in constant readiness, the Army's Airborne Rangers are ready to be deployed to any corner of the globe at a moment's notice. What? They're like real live G.I. Joes, and can perform just about any task set for them, from air assualt to search and rescue.
6. Marine Corps Force Reconnaissance
These guys are the best in the world at going behind enemy lines. They're primarily tasked with collecting intelligence, but can be engaged in direct action if need be.
7. Night Stalkers
These guys are the unit of the Army that fly the helicopters that get special forces personnel to their destination. They're a highly elite group trained at moving at high speed and low altitude. They most recently flew troops for the raid on Osama bin Laden's compound.
The Special Activities Division (SAD) of the CIA are engaged in both clandestine political action and paramilitary special operations. What does that mean? That officially, they don't exist. If they're compromised during an overseas mission, the government will officially deny any knowledge.
9. The Activity
Also known as the United States Army Intelligence Support Activity (USAISA), these are the guys who go out and collect intel for many of the other top Special Ops groups in advance of missions. These guys are so secretive we don't even know what their current name is.
10. 24th STS
The 24th Special Tactics Squadron is one of the premiere Special Missions Unit of the U.S. Airforce. Made up primarily of combat controllers and parajumpers, they're shrouded in secrecy, but are thought to be the Airforce's branch in the Joint Special Operations Command (JSOC).