The setting is modern and very Earth like in many ways (technology level being one of them).
In one of the largest nations--first world, high GDP, respectable per capita income--there exists this odd (and very unstable) political system where the elected political parties are allowed law enforcement representation proportionate to their congressional representation. Each officer by-the-book reports up the chain of command, but in practice each officer is loyal to his or her party first and foremost.
The uniform of these officers has varied over the years, but typically is a long coat (double breasted buttoned, but may be left unbuttoned) made of thick wool with thin and small ceramic ballistic plates* under the clothing, reinforced with Kevlar (cosmetically hidden). The uniforms are thus somewhat stiff, but cans till bend and move as the officer walks. A knee shoved up would still show as a lump protruding up.
Due to a now twisted, heavily modified, and generally warped law once meant to encourage peace, officers aren't allowed to openly carry firearms (or other weapons), but they are allowed to conceal carry firearms. Thus a strange political dance has developed.
The standard (set by the courts) is that if another officer can tell that an accused officer is carrying, that is sufficient evidence that the accused was open carrying, and did not properly conceal his firearm.
Thus one officer accuses another officer of carrying and is right, the accused is stripped of badge. If the accuser is wrong, he is stripped of badge. The removed officer leaves a hole that cannot be filled until the next election cycle, so it's important not to have another enemy officer catch you with a firearm, and it's important not to falsely accuse another.
Despite these risks, accusing of carry a weapon is the fastest, easiest, and cleanest way of reducing the opposing party's law enforcement, and thus guns on the street. (Citizens are not allowed to possess firearms)
Efforts to trick another into thinking that one is carrying but not actually carrying (hiding a large lump under one's clothes, walking in a suspicious manner) to gain a false accusation will normally be appealed in the courts, where typically the judge rules against the trickster. This ruling isn't perfectly consistent, but historic cases have shown that the tactic of pretend-carry is generally riskier than it is worth.
There has begun to be an arms race of trying to hide increasingly militarized weaponry under their uniform as secretly as possible. They have no fear of being stopped to be searched (with their legal authority they can just deny the request), so they just need to make it as impossible-as-possible to determine if they're carrying.
Only very rarely is their actual open conflict between law enforcement (rare enough that one or two dead offices makes national headlines), but every side agrees that it's only a matter of time before it will devolve into open war.
Further, since everyone expect the first rash of violence to start and be over very quickly (well under an hour, country wide, as the news of open conflict spreads over the country's news and computer networks), every party wishes to keep as many officers armed, and those officers as armed as possible.
Naturally a certain percentage of unarmed officers need to be kept unarmed to discourage (and punish) false accusations of carrying.
As the arms race evolves the parties will gravitate to equipping more and more militarized weapons. This escalation period is short enough that weapons can't be specifically designed and manufactured for this purpose. The firearm variety and nature of arms is very comparable to Earth's own, and can be considered identical for purposes of this question.
What sort of weapons would make the most sense for the parties to equip their officers with, and how large is the reasonable maximum physical weapon size for these officers to conceal and carry?
