An Armored Car is a wheeled, armored Vehicle, typically carrying a heavy machine gun. It can also carry a small number of infantry inside in relative safety. Armored cars are largely resistant to small arms fire, but are still vulnerable to all large-caliber and explosive weapons.
Armored cars are very fast relative to heavier vehicles, and can be used to transport troops quickly into, out of, or around the battlefield. Their primary purpose however is to support the troops with some heavy firepower once they've dismounted. Armored cars are not capable of engaging the enemy safely on their own, without infantry support.
The majority of Armored cars in Arma and in the real world are OPFOR vehicles. Of particular note are the Vodnik and BRDM. Both appear frequently in missions as AI-controlled opponents that pose a small but credible threat to friendly infantry. They are very rarely seen operated by players due to their high vulnerability and limited combat effectiveness.
Armored cars are similar to armed recon vehicles, except they are better-armored. BLUFOR fields recon vehicles instead of armored cars (the HMMWV being the most common variety), and those are significantly more common as friendly-controlled vehicles.
Specifications
An Armored car is an armed, wheeled vehicle that is suitably protected against most small arms fire - but not sufficiently armored to withstand most other weapons. Armored cars occupy a niche between recon vehicles (which are vulnerable to small arms) and APCs (which are impervious to small arms).
Armored cars typically have either 4 or 6 wheels. Though the most common model (the BRDM) has 8 wheels in total, it only uses 4 of them in most circumstances (and never uses 8 in ArmA). It is very fast compared to APCs and especially to tracked vehicles, making it useful as a quick transport or flanking vehicle.
The armor of an armored car can reliably withstand bullets of diameters not exceeding 7.62mm. Though such bullets can occasionally find their way past small opening in the armor (such as the driver's vision slits), they are highly unlikely to do so. Even the vehicle's tires are resistant to small caliber bullets, and any windows are bullet-resistant as well. Heavier bullets, like .50 Cal (12.7mm), can occasionally penetrate the armor itself. Explosive weapons, including hand grenades and HEDP shells, are both likely to damage the vehicle upon a direct hit, and can destroy it with a sufficient number of hits.
Armored cars carry at least one heavy machine gun as their primary weapon. Some models have additional medium machine guns to augment firepower against individual infantry targets at close range. These weapons can make the armored car dangerous if isn't destroyed quickly.
Armored cars can carry a fireteam of passengers. They may be called on to do so when entering the battlefield, when leaving it, or when there is a need to quickly move men to another location. Speed is the only real advantage to this maneuver, as the armored car provides relatively little safety to the men inside compared to traveling on foot, making a single target instead of several smaller ones.
Overall, armored cars are little more than a highly mobile heavy machine gun platform designed to augment the infantry's firepower, and to quickly flank and surprise enemy infantry. Due to the armored car's vulnerabilities, it cannot effectively act on its own without the element of surprise, and therefore requires the infantry's reciprocal support in order to remain effective.
Models
There is only a handful of armored car models available in ArmA, or indeed in modern warfare at all. Only three are generally seen.
The most common is the BRDM. This OPFOR armored car straddles the line between armored cars and armored personnel carriers, being fairly well-armored. The BRDM has 8 wheels, although four of them are tucked up underneath the vehicle's belly (in real life they are extended to help negotiate difficult terrain). The BRDM has a KPVT heavy machine gun installed in a closed turret, as well as a PKT medium machine gun for use against single infantry targets. BRDMs are very common as AI-controlled opponents, typically heralding the arrival of more powerful enemy vehicles.
The Vodnik, another OPFOR armored car, was quite common in the ArmA 2 era, but disappeared for several years following the move to ArmA 3 before being reintroduced via modifications. It has 4 wheels, and is a little smaller and less well-armored than the BRDM. The Vodnik is a classic armored car, matching the specifications listed above. It carries the same weapons as a BRDM. The Vodnik's gunner is exposed when using the vehicle's main gun, and thus is significantly easier to kill. Vodniks were also very common as AI-Controlled opponents during the ArmA 2 period.
NATO armored cars are significantly rarer, with only one model being prominent in the ArmA 3 era: the MRAP. These heavy trucks are specifically designed with enough underbelly armor to withstand IEDs. MRAPs come in multiple varieties in real life, but the most commonly used one appears to be mostly the American 6-wheeled model with an M2 Heavy Machine Gun turret. They have only appeared as player-controlled vehicles thus far, and even then are rare. Far more common is the HMMWV vehicle.
Another, rarer NATO model appeared with the RHS USAF mod: the V-1117. This car is significantly better armed, with a flat turret carrying a Mk 19 automatic grenade launcher as well as an M2 heavy machine gun, making it the most dangerous armored car so far in terms of overall firepower. It is otherwise similar to the BRDM.
Organization
The vast majority of armored cars are AI-controlled enemy vehicles; Player-controlled instances are comparatively very rare.
Nevertheless, armored cars are used in a similar manner as armored personnel carriers, including the way they were organized as part of the friendly force. This is not surprising, given the similarity (and sometimes overlap) between armored cars and APCs. However, due to the lighter armor of armored cars compared to APCs, their combat role is somewhat limited. Their primary advantage - being able to maneuver very quickly without fear of enemy small arms - if having capacity for troops, it is utilized to quickly transport infantry from place to place, mainly along a single road (as a Convoy). Like APCs, each armored car is typically attached to a single squad, and is responsible for transporting and supporting that one squad.