Trench Coat Warfare

Someone allows his or her Badass Longcoat to flare open, revealing enough guns to fuel a small terrorist group's assault on Capitol Hill. Things just got a lot more interesting.

Compare with Hyperspace Arsenal and Coat Full of Contraband. Often overlaps with Throw-Away Guns. Will likely precede an Oh Crap moment.

Anime and Manga

 * Pierrot Le Fou from Cowboy Bebop.
 * Meryl Strife from Trigun did this to an extreme, with dozens of one-shot derringer pistols lining her cloak, which she'd go through quite rapidly in a gunfight.
 * Variant in The Castleof Cagliostro: Lupin, shortly after ripping off the false beard, mustache, and glasses from his disguise as the archbishop, is about to be rushed by the Count. He then dramatically throws open the robe to reveal dozens of lit fireworks, all of which launch and begin going off, causing chaos and confusion. Jigen and Goemon (used to Lupin's talents for causing mayhem) take advantage of it to go on the attack, Jigen opening fire on the Count's assassins with a World War II anti-tank rifle and Goemon cutting their armor open with his super-sharp sword. Zenigata storms the castle with several Interpol troopers and they get into a fight with the royal guard.
 * Sayaka from Puella Magi Madoka Magica does this with her cape to create swords, which she then throws. Mami does this with her Magic Skirt (no, it doesn't look like how you think it goes).
 * In Read or Die, Yomiko Readman's coat is filled with newspapers, magazines, paperbacks, and other forms of reading material. While most of the time this is due to her being an obsessive bibliomaniac, her powers as a Paper Master allow her to wreak a lot of havoc with all that reading material if she has to.
 * In one episode of Pokémon, a doctor opens his lab coat to reveal an arsenal of scalpels, syringes, and other instruments of medical pain as he tells Team Rocket exactly why it would be unwise for them to try to steal the Pokemon that have been temporarily been placed under his care.
 * Ryouma in New Getter Robo opens a cloak halfway through the series, revealing an arsenal of pointy and sharp objects on his person.
 * In The Slayers TRY, Jillas, a comic relief Anti-Villain and a parody of The Gunslinger, demonstrates this trope with a cloak.

Comic Books

 * The Punisher has done this upon occasion.

Film
"(Neo steps through a metal detector, setting it off.)
 * The most famous example of this is Neo in the first The Matrix movie.

Security Officer: Please remove any metallic items you may be carrying: keys, change...

(Neo opens up his coat, revealing a massive weapons stockpile.)

Security Officer: Holy shit!"


 * The Boondock Saints features Il Duce, who reveals six pistols under his coat just before the firefight with the title characters.
 * The titular character in V for Vendetta at one point draws back his cape to reveal multiple knives. He goes on to win a gunfight.
 * Machete carries a ludicrous number of knives in his trenchcoat.

Video Games

 * The Merchant's introduction in Resident Evil 4 - he can carry as much stuff within his coat as he can sell to Leon, and it shows.
 * In Epic Battle Fantasy 3, the Gunslinger enemies and their sword-based variant essentially ARE trench coats with robotic heads. The coats don't open, although just because it'd require an explanation on how hammerspace works - BFGs or BFSs still emerge from the coats regularly.

Web Comics

 * In a variation: Evil Chancellor Magon during the 'Stormbringer' arc of Sluggy Freelance. Seeing as it's the middle ages, he doesn't have any guns or trenchcoats - he does, however, have several daggers lining the inside of his cloak. All the easier to to indulge in his Chronic Backstabbing Disorder. (Though he prefers the term 'Morally Challenged'.)
 * And in another case, one character accuses Riff of bad intentions towards another character by asking if he had A weapon beneath his trench coat. Kiki the ferret jumps out from the coat replying that it wasn't just one gun, it was an arsenal.

Web Original

 * Sniper, from the Global Guardians PBEM Universe.
 * Parodied this fake movie trailer, albeit with a hoodie instead of a trench coat, and... spoons instead of guns.

Western Animation

 * Variant in the animated show COPS. The villainous Buttons McBoomBoom opens his coat to reveal machine guns hidden inside his chest.