Not all weapons are fit for covert action. Here is some history and some facts:
1. Weapons - Hand (Knives, Coshes, etc.) 2. Weapons - Firearms - Special Purpose & Hidden 3. Weapons - Firearms - Generic 4. Weapons - Chemical
Contrary to popular belief, your everyday garden variety spy does not often, if ever, use weapons. Most spies are more likely to be office workers or low ranking officials than bloodthirsty commandos, especially in industrial espionnage. Attracting attention by violent action, and the danger of discovery it presents is too great a risk, especially if one has no training in such matters. Also, cadavers are (literally) a drag to get rid of.
Be that as it may, some spies are not bound by such restriction and are trained to exert deadly force to achieve their objectives or save their lives.
Weapons - Hand (Knives, Coshes, etc.)
The celebrated British SOE (Special Operations Executive), founded in 1940, and later its American equivalent the OSS (Office of Strategic Services, 1942), both spent the war years inventing ingenious devices to, among other things, deal discreet death to the enemy. This was the starting signal for generations of technicians in all camps competing in originality and design. They spawned the prototypical “Q branch”.
The Fairbairn-Sykes was a knife especially designed for fighting. Spies and commandos were trained in its use with a blunted version before being dropped behind enemy lines. Some other knives were so small they could be hidden behind lapels. Coshes were produced and distributed as well as garrottes, some of which were hidden in and passed off as condoms. A rather clever weapon, the Peskett, combined cosh, garotte and dagger (but no condom). Brass knuckles were also fused with knives in a deadly combination, and small cruciform blades were hidden inside pens and pencils, which brings us to :
Weapons - Firearms – Hidden, Special Purpose & suppressed
Small, mostly single-shot guns were designed to be strapped to the wrist, hidden in belts and gloves, in cigarettes, cigars, pipes and pens, flashlights and even toothpaste tubes. The KGB engineered a gun that could be hidden in a spy’s rectum. Most of these weapons were designed to evade search, for use as a last resort after capture.
Allied forces manufactured a small .45 calibre gun called Liberator for mass air drop in occupied France, thinking that the idea of an armed population would demoralize the enemy. Didn't work. Its successor, the Deer gun. was meant to be airdropped to South Vietnamese guerrillas, who were supposed to use them to acquire the enemy's vastly more efficient weapons. Didn't work either. In both cases, because of the time needed to reload the weapon, a misfire or missed shot guaranteed that you were a dead man. Both guns barely saw any action.
Dart pistols and crossbows didn’t see much action either. Except for the Big Joe crossbow, tech labs mostly abandoned their development when the suppressor was invented.
Suppressors (or silencers) are not all as silent as they’re made out to be. Although Ian Fleming once said that a silenced Sten sub-machine gun hardly made a whisper, the vast majority of suppressors might not be noticed in the din of today's downtown rush hour traffic, but would raise alarm in slightly quieter environments.
Firing a weapon produces five different kinds of sounds : the hammer / firing pin impact, the explosion of gases coming out the end of the barrel, the supersonic crack of the projectile, the weapon reloading itself (auto and semi-auto), and the round hitting (or missing) the target.
While the hammer / firing pin noise cannot be suppressed, the reloading sound can be addressed by simply cancelling the ejection cycle.
As for the two loudest sounds, the first is the supersonic crack and can be eliminated by using less gunpowder in the cartridge, thereby making the round subsonic. The second is that of gases rushing out of the barrel. Suppressors diminish the sound of the explosion by trapping it inside small chambers.
As for the last remaining sound, that of the round hitting the target, they say you never hear the shot that kills you...
Few revolvers ever were equipped with a suppressor ; the Russian Nagant and the Stechkin are among the rare exceptions. The Nagant’s cylinder moves forward and closes the gap to the barrel as part of its firing cycle, thereby directing all sound to the suppressor at the end of the barrel, much like a pistol. The Stechkin is a somewhat odd revolver, and uses special “silent” ammunition.
Firearms - Generic
If a spy has to carry a regular pistol, the first rule is that it has to be easily concealed. Small and flat (flat as in single column magazine) would be just about right. A revolver's hammer snagging on your clothes when you’re drawing is not an option, although the S&W Centennial was created with a hidden hammer to avert that problem, as was the Colt Bodyguard. A revolver may carry fewer bullets than a pistol and fire at a slower rate, but they are infinitely less prone to jamming than pistols.
You'd think that a covert operative would be armed with whatever weapon that was found to be reliable in his country's own military, but this would invariably point to his country of origin. CIA contractual operative and ex-special forces weapons expert Raymond Allen Davis allegedly killed two alledgedly shady Pakistani characters with either a Glock 9mm or a Beretta. Not a Colt.
In one of the Bond movie, 007 falls prey to a cloud of knockout gas emanating from a cigarette he was about to light for a lady. This is not a fantasy from a spy fiction writer running out of ideas, but a real weapon invented during the Cold War by the KGB. They also used poisoned umbrella tips and came up with all sorts of other ingenious assassination devices.
Polonium is a highly radioactive chemical that was recently used to assassinate a Russian dissident, Alexander Litvinenko.