Officially, of course, the Watch-Dogs do not exist. They are a top-secret 'Full Black' unit which has no budget, no home base and no command structure. If one were to dig a little, one would find that they are a fifty-man test unit, trialling newly developed exo-armour suits which incorporate the most highly advanced visual and sensor suites in existence. The 'Dogs, as they are nick-named by those who are "in the know" also field test new weaponry systems being researched by a number of leading defense contractors. Their armour's systems allow interface and operation of weaponry a standard-issue soldier would not be able to.
That is the "unofficial-official" version, of course; I see that you are learning. The obvious answer is not, necessarily, always the right one, at least not where Lucifer is involved. Lucifer is, of course, involved here, indirectly at least. In truth, the Watch-Dogs are the personal bodyguard of Abaddon and are not human at all but a group of carefully hand-picked nephilim from Atlantis. That's what Abaddon tells people, at least. The truth is that nobody knows because the 'Dogs have never been seen without their helmets by anyone, it is said, except Abaddon.
The name of this unit is actually a joke, or at least it started as one. Asmodeus will often refer to Abaddon as "Lucifer's Dog" because the big man will follow his boss's orders without hesitation or question. He will follow his 'master' like a 'good dog' as Asmodeus likes to put it. Therefore, he famously quipped, those who watch the dog are Watch-Dogs, right? Hardly anyone laughed. Penuamael may have smiled though he passed it off as gas caused by the rich food.
Abaddon is not, contrary to popular opinion, completely lacking in a sense of humour and the name, which he actually liked (though he never admitted this to Asmodeus) stuck.
The Watch-Dogs were first officially seen as an actual unit around 12th Century AD in Spain. They were later seen when the outlaw known as Robin Hood tried, unsuccessfully, to ambush the caravan of Bishop Abingdon, Abaddon's host at the time. In those days they wore heavy plate armour of enamelled black steel with a 'kettle' or 'crusader' style helmet. They also carried coffin or bulwark shields of steel-bound oak. All their equipment, from broadsword to belt was midnight black, even the device in the centre of their shield was only visible from the right angle, due to it being a deeper black then the surrounding shield. They were never seen in the field in their full half-century, only ever a squad or two, more were rarely needed. In those days they were renowned as some of the very best swordsmen in existence; fast, brutal and disciplined.
Today their brutality and disciple have not changed, only their equipment has. Each is armoured in a KALOS exo-suit; made of advanced nano-materials and high-impact/ablation alloys of unknown composition. Each suit weights close to 200lbs so it is assumed the 'Dogs are very strong to spends long hours on guard standing upright in full kit. Standard armament is a custom carbine of unknown manufacturer. The weapon looks like something of science fiction and nobody knows how it works. It is assumed that anyone who has seen such weapons in action did not survive the experience.
Also, the sight is a strange affair; it is hypothesised to contain vIR (Visible Infra-red), EMR (Electromagnetic Radiation) sensors, tritium coating, FoC (Fibre optic Collectors) among other suites we cannot determine. The major difference between this and other sights is the lack of an eyepiece; all information is beamed directly to the 'Dog's helmet-mounted optical suite.
The five-lens configuration of helmet-mounted optics is something which makes the 'Dogs unique and immediately identifiable. They are often jokingly referred to as the 'spiders' for the excess of eyes. Though different 'Dogs vary the configuration of their optics, dependant on their needs, there are always five elements no more and no less. It is assumed these lenses operate like traditional NV/IR (Night Vision/Infrared) systems used by units such as Navy SEALS etc. However, there has been no success in determining what it is that causes that purplish-pink glow which seems to radiate from the lenses.
It is rumoured that a 'Dog unit tracked a target in complete darkness, during a power failure on the lower levels of a subterranean base. They tracked the target in complete blackness while their lenses glowed like "a quintet of hellish purple eyes" in the dark. Who the source of this account is will not be revealed by this report, though their identity is known to us.
There - again with the fives - are a total of FIFTY Watch-Dogs; never more and never less. These fifty are organised into ten-man squads. A Watch-Dog had no name, only a designation. Organisation goes as follows;
Squads or Packs: Alpha - Kappa. Alpha Squadron is known as the "Dog-House Guard" and never leave Abaddon's immediate vicinity. Squads Beta-Kappa operate regular patrol and sentry duty. One curious detail is that 'Dogs will, no matter what their duty, operate in pairs. They will guard either side of a doorway or patrol side-by-side. Never has a Watch-Dog been seen on their own.
Designations: 'Dogs receive a numbered designator which is usually tied with squad identifier. For example; Watch-Dog Beta-Two (WD-B-2) for number two man in Beta Squadron/Pack. The only exception to this rule applies to Alpha-Pack members. In their case, the pack name is left out of the designator. Thus we get Watch-Dog One etc. There are no ranks in the Watch-Dogs it is supposed that the higher a 'Dog's number the higher his 'rank'.
Finally, we touch on the big question we are sure you are asking; attrition. Yes, the 'Dogs are a kind of nephilim which remains unidentified and is, therefore possessed of unknown abilities. True they are armoured by the most highly advanced combat and protective systems on Earth; which are likely to be techno-mystic in nature, of course. All this and more is accurate but "generals lie and soldiers die" as the saying goes. There is a version of the Robin Hood ambush in circulation which is heavily denied at the highest level. It is implied that Sable was present at the ambush and that he, in coordination with Robin, accounted for four Fallen and twenty Watch-Dogs, as well as uncounted regular human guardsmen. It is said that Sable caused deep and lasting shame to his "father" as well as Asmodeus, Penumael and Sammael. He is also said to have stolen some rather valuable items. It is said but also rather quickly denied.
Sable killed twenty Watch-Dogs, almost half of a half-century of the best. Where did the others come from? How do casualties get replaced? There is no record anywhere of any form of recruitment efforts or process. Nobody suddenly goes missing or disappears for a while them refuses to speak about it. Watch-Dog One is said to be the same 'man' who guarded Abaddon in Atlan.