Briefcase Blaster

Note the trigger in the briefcase handle.

A gun concealed inside or in the shape of a briefcase.

Most of the examples under IKEA Weaponry pack away into a briefcase when disassembled, other than those deliberately disguised as something even more innocuous.

Turns out to be a case of Truth in Television. The CIA, as well as American government and military bodyguards, do actually use submachine guns concealed in cases (just like the one depicted). The case is built with a trigger on the handle that allows it to be fired without removing the weapon.

See also Senseless Violins, when weapons are concealed in an instrument case, and Handbag of Hurt, when the briefcase itself is used as a melee weapon.

Examples of Briefcase Blaster include:

Anime and Manga

Black Lagoon: Roberta uses a machinegun briefcase in her initial appearance.
Used by a pair of bodyguards in the opening scene of Ghost in The Shell.
- The briefcases also make an appearance at the end of Ghost in the Shell: Stand Alone Complex being carried by the American Empire agents who are accompanying Gouda in the final episode of season 2.
Black Cat If you see the Badass Normal sidekick coming towards you with a briefcase, RUN. If you find out what is in it, you are probably already dead. (He has at least 5 ways to kill a person built into that thing by the end)
Kazuki in Ga-Rei Zero dual wields anti-demon machinegun briefcases. Also, this trope is somewhat similar to Senseless Violins, except that the carrying case is the weapon.
This is the preliminary weapon of The Invaders in Gate Keepers, to go with their identical suit-and-tie motif.

Film

The Trope Codifier may be James Bond's briefcase in From Russia with Love, which is the first real Bond gadget. Amongst its other tricks, it features a rifle folded up inside and a tear gas booby trap.
- The videogame replaces this with the Briefcase Turret (see the "Phoenix Ronin" entry below). It's Q's briefcase, but with an automated turret and photoelectric sensor (like the kind you see on those tapless sinks in McDonald's). The kicker: once deployed, it cannot be retrieved.
In Judge Dredd, a prison warden hands Rico a small case containing Rico's old badge. Rico quickly reveals that the case itself is a reconfigurable handgun in disguise. Why the warden handed his most dangerous prisoner a package without inspecting what was inside it is a Wallbanger that is never explained.
RoboCop 2. As Hob is escaping he's carrying what appears to be a small metal briefcase. When confronted by Officer Lewis he unfolds it into a machine gun and tries to shoot her. It's an actual weapon, the Ares FMG
In Iron Man 2, Tony has a briefcase that converts into an entire suit of armor. This is straight out of the comics too (although there, the armor is usually stored inside the briefcase). To really get into this trope, one action figure of this armor—the Mark V--has a briefcase that becomes a missile launcher.
In The Replacement Killers, the back-up hitmen used the MP5 briefcase described below.
These come in handy in the first Alien vs. Predator film.
In the Jet Li film Romeo Must Die, the bodyguard of the Corrupt Corporate Executive keeps an assault rifle in a briefcase. The handle of the briefcase is actually the rifle's rear sights.
Faster: The Nameless Professional Killer is shown packing a suitcase with strapped-in guns and knives.
Highlighted in Lord of War, when Yuri quips how easy disguising weapons in camcorder cases was in the 1980s due to the size of camcorders.

Literature

In Snow Crash, Reason is mounted inside a suitcase, though it does have a heat exchanger coming out of the side.
The Executioner: while posing as a drug dealer's bodyguards, Able Team are each equipped with a briefcase with an Uzi inside and a steel trauma plate for protection. "If you see a bullet coming, just block it."

Live Action TV

Maxwell Smart had one of these once, as did his inspiration, James Bond.
- First seen used by a KAOS-affiliated hit man played by Leonard Nimoy.
Kamen Rider Decade had a card case which could extend a handle and barrel to be used as a gun. It could also extend a blade to be used as a sword.
Deadliest Warrior: One of the weapons used by the CIA in CIA vs. KGB is a Walther PPK hidden in a briefcase with a pulley system (terminating in a string looped around the finger) attached to the trigger. The agent assigned to test it manages to shoot all three targets perfectly while carrying the case normally.

Tabletop Games

In the Hot Chicks RPG, the Trick Case can fire a weapon while it's inside the briefcase. The Discarding Case has a hidden switch that causes the case to fall away, leaving the weapon in the user's hand.

Video Games

The N64 game Perfect Dark had the laptop gun, which could also double as a turret.
007: Nightfire has the Phoenix Ronin, a minigun concealed inside of a briefcase that can be set down as an automated sentry gun or operated by remote.
The House of the Dead spinoff Zombie Revenge featured the two guitar-case weapons from Desperado
The Pandora gun in Devil May Cry 4 is carried around like a briefcase. It can turn into a crossbow, a bazooka, a laser cannon, a minigun-version of the more realistic Briefcase Blaster shown above, a blade boomerang and a mobile missile launching fortress, and when opened, it produces a brilliant flash of light that instantly destroys all enemy shields in addition to damaging them. It also has 659 other forms as well, but naturally, you'll never actually see any of them in gameplay. See more here.
The 'Sniper Case' from the Hitman games allow you to carry a disassembled Sniper Rifle around in a briefcase without suspicion, as sniper rifles are too large to be concealed in 47's jacket.
- There are also a few other suitcases for other types of rifles. Also a subversion as these suitcases are so long that somebody should be asking questions.
Secret Agent Clank goes one step further and gives us the Blowtorch Briefcase.
No One Lives Forever has the rocket-launcher briefcase.

Western Animation

In the Swat Kats episode "The Dark Side of the SWAT Kats", the evil Mirror Universe version of Deputy Mayor Briggs had a gas gun in her briefcase. She used it knock out two guards so she could release what she thought were the in-universe evil Swat Kats.
Samurai Jack: in "Jack and the Labyrinth", the stranger carries a multipurpose briefcase that has a machine gun inside as well as a lighter.

Real Life

Truth in Television: Heckler and Koch makes a special briefcase for their MP5K. Here's a video.
Magpul made a concept product that looked similar to a small briefcase that housed a Glock and a flashlight and could easily fit into your back pocket. All you had to do was flip it open and you'll be ready to go. Magpul makes a near-identical kit for airsoft guns, but the real one never reached the production stage.
The CETME Ameli is a light machine gun, 5.56mm caliber, capable of fitting inside a briefcase. Unlike the above examples, it does have to be removed and assembled before use, but that is surprisingly quick.
During the assassination attempt on former President Ronald Reagan, Agent Robert Wanko pulled an Uzi out of his briefcase in order to cover the President's evacuation to the hospital moments after the President had been shot.
The Ares FMG appears to have this idea in mind.
The Nerf Deploy CS-6 is a pump-action blaster that can collapse into a compact "briefcase" form.
Beyond 2000 featured a concept of a very rapidly firing submachine gun with a Laser Sight, the AM-180A, based on the American 180 submachine gun (distinctive for its saucer shaped pan magazine mounted on top of the weapon and the secret to its very high rate of fire), which not only made for deadly accurate shots, but also fired so rapidly it could shred most materials to bits and even penetrate bulletproof vests. A concealed version was developed in parallel, being built in to a briefcase that even included the Laser Sight, and like the pictured weapon above, could be fired with the case closed (in fact during the show, the briefcase version was used to demonstrate that a bulletproof vest was futile in protecting the victim from this weapon).
- The standard/non-concealed version of the AM-180A also happens to be IKEA Weaponry, and was designed to be easily assembled in complete darkness.
While SMGs and the like really do utilize this trope, one way fiction often misrepresents it is with long-range sniper rifles that disassemable to fit in a briefcase. Such weapons are very precisely fine-tuned and the disassembly and reassembly process would throw even an experience sniper off - it doesn't take much to miss when firing at a target thousands of feet away.