"The Dirty Half Dozen" is the nineteenth episode of the second season of the American television series "Agents of S.H.I.E.L.D.", based on the Marvel Comics organization S.H.I.E.L.D. (Strategic Homeland Intervention, Enforcement and Logistics Division), revolving around the character of Phil Coulson and his team of S.H.I.E.L.D. agents as they infiltrate a Hydra base to rescue two of their kidnapped allies.
 It is set in the Marvel Cinematic Universe (MCU), sharing continuity with the films of the franchise.
 The episode was written by Brent Fletcher and Drew Z. Greenberg, and directed by Kevin Tancharoen.
H.A.M.M.E.R. is a fictional espionage and law enforcement agency appearing in American comic books published by Marvel Comics.
 The organization is led by Norman Osborn and was formed in "Secret Invasion" #8 to replace S.H.I.E.L.D. The organization plays a large part in Marvel's "Dark Reign" and "Siege" storylines that ran from 2008 - 2010.
S.H.I.E.L.D. is a fictional espionage, special law-enforcement, and counter-terrorism agency appearing in American comic books published by Marvel Comics.
 Created by Stan Lee and Jack Kirby in "Strange Tales" #135 (Aug. 1965), it often deals with paranormal and superhuman threats.
The World Counter-terrorism Agency (commonly known as the W.C.A.) is a fictional anti-terrorist organization appearing in American comic books published by Marvel Comics.
 The organization first appeared in "New Avengers: The Reunion" #1 (2009) and was created by Jim McCann and David Lopez.
 The acronym W.C.A. is a homage to the West Coast Avengers, a title that prominently featured Hawkeye and Mockingbird.
Symkaria is a fictional Eastern European country appearing in American comic books published by Marvel Comics.
 The country was created by Tom DeFalco for the Marvel Universe.
 It is one of several fictional countries in Eastern Europe created for Marvel Comics.
 The fictional country is mostly known as being the home of Silver Sable and the Wild Pack team though it is used throughout the Marvel Universe.
 The country has appeared in issues of "Silver Sable", "Silver Sable and the Wild Pack", "The Amazing Spider-Man", "Thunderbolts", "Citizen V and the V-Battalion", and other comics published by Marvel Comics.
S.T.R.I.K.E., an acronym for Special Tactical Reserve for International Key Emergencies, is a fictional counter-terrorism and intelligence agency appearing in American comic books published by Marvel Comics.
 The organization often deals with superhuman threats, and was introduced in "Captain Britain Weekly" #17 as the United Kingdom's counterpart to the United States' anti-terrorism agency S.H.I.E.L.D.
Captain America is a fictional character appearing in American comic books published by Marvel Comics.
 Created by cartoonists Joe Simon and Jack Kirby, the character first appeared in "Captain America Comics" #1 (cover dated March 1941) from Timely Comics, a predecessor of Marvel Comics.
 Captain America was designed as a patriotic supersoldier who often fought the Axis powers of World War II and was Timely Comics' most popular character during the wartime period.
 The popularity of superheroes waned following the war and the "Captain America" comic book was discontinued in 1950, with a short-lived revival in 1953.
 Since Marvel Comics revived the character in 1964, Captain America has remained in publication.
X-Factor Investigations is a fictional detective agency appearing in American comic books published by Marvel Comics.
 The organization was created by writer Peter David for the comic book series "X-Factor" (vol.
 3).
 The agency first appears under the name XXX Investigations in the first issue of the Marvel Comics limited series "Madrox" #1 (November 2004).
 In the final issue, "Madrox" #5 (March 2005), the name is changed to X-Factor Investigations, and later abbreviated XF Investigations.
Namor the Sub-Mariner ( ) (Namor McKenzie) is a fictional character appearing in American comic books published by Marvel Comics.
 Debuting in early 1939, the character was created by writer-artist Bill Everett for Funnies Inc., one of the first "packagers" in the early days of comic books that supplied comics on demand to publishers looking to enter the new medium.
 Initially created for the unreleased comic "Motion Picture Funnies Weekly", the Sub-Mariner first appeared publicly in "Marvel Comics" #1 (cover-dated Oct. 1939) – the first comic book from Timely Comics, the 1930s–1940s predecessor of the company Marvel Comics.
 During that period, known to historians and fans as the Golden Age of Comic Books, the Sub-Mariner was one of Timely's top three characters, along with Captain America and the original Human Torch.
 Everett said the character's name was inspired by Samuel Taylor Coleridge's poem, "The Rime of the Ancient Mariner".
 Everett came up with "Namor" by writing down noble sounding names backwards and thought Roman/Namor looked the best.
The Angel (Thomas Halloway, often shortened to Tom Halloway) is a fictional character, a superhero appearing in American comic books published by Marvel Comics.
 Created by artist Paul Gustavson and an unconfirmed writer during the Golden Age of Comic Books, the Angel first appeared in "Marvel Comics" #1 (Oct. 1939), the first publication of Marvel Comics' predecessor, Timely Comics.

Question: "The Dirty Half Dozen", the nineteenth episode of the second season of an American television series based on what Marvel Comics organization, a fictional espionage, special law-enforcement, and counter-terrorism agency appearing in American comic books published by Marvel Comics?
Answer: S.H.I.E.L.D.