RPG-18, RPG-22 and RPG-26 are Soviet designed and Soviet made anti tank weapons. Contemporary to popular belief, in this case RPG does not stand for "rocket propelled grenade" or even "hand held anti tank grenade launcher", as it would be with the RPG-7 or it's derivatives. In case with these disposable RPG-18/22 tubes it actually stands for "hand held anti tank grenade". Because essentially it is what it is - just a single use grenade.
If you are really into RPG-18 and other Soviet disposable grenade launchers, do not hesitate to check out publication on the Soviet Infantry Weapons of the Afghan War.
History of Soviet disposable anti-tank grenades
The RPG-18 is a disposable anti-tank rocket launcher that was developed and adopted by the Soviet Union in the early 1970s. It is very likely that the concept was taken from the American M72 grenade, which was used excessively in Vietnam.
The new Soviet tube was long overdue for the potential full scale war. By the end of 1960s, Soviet infantry antitank capabilities were somewhat limited, especially in the small units. An infantry section could definitely rely on at least one RPG-7 (or RPG-2). If the section was equipped with BMP-1, their anti tank potential was decent, but not many infantry units did feature a BMP at this point. The majority was armed with BTR-60 or older vehicles.
A single soldier, if not a grenadier, had something to fight tanks, as well. It was a RKG-3 hand throwable anti tank grenade. These were the weapons of last resort, as to use it effectively one had to get at a distance of 10-20 meters to the enemy armor. They were effective though - as by the design it would land on top of the tank, where the armor would be the weakest.
Hand held anti tank grenade - RPG-18
The RPG-18 was a huge technological leap forward, compared to RKG-3 grenades. It now gave the ability to fight tanks and armored vehicles at distances of between 100 and 200 meters, which is way better than jumping under the tank with a RKG-3. Moreover, Being relatively cheap and light, these could be supplied to the infantry units in almost infinite numbers.
And this is precisely what happened. These grenades were produced in such big numbers, that even though the production finished by the end of 1980s, the stocks of RPG-18s only started to run out across the globe in early 2020s.
As it turned out, this grenade would not work well against modern tanks, though it did could easily penetrate and destroy other armored vehicles. It also worked great against regular cars and trucks, as well as it could have some impact on light fortifications.
The RPG-18 itself consists of a launcher tube made of fiberglass and a warhead containing a shaped charge that is capable of penetrating armor. The launcher tube is designed to be discarded after use, making the RPG-18 a "one-shot" weapon.
The RPG-18 is a lightweight and compact weapon, weighing just 2.5 kg (5.5 lb) and measuring 72 cm (28 in) in length. It can be fired from a standing, kneeling, or prone position, making it suitable for use in a variety of combat scenarios.
The RPG-18 has a maximum effective range of 200 meters (656 ft) and can penetrate up to 375 mm (14.8 in) of rolled homogeneous armor (RHA) or 500 mm (19.7 in) of concrete.
RPG-18 in Afghanistan
The RPG-18 have seen its fare share of combat use in Afghanistan. It was available in big numbers to troops of all branches and they never minded to use it. It has its advantages when compared to RPG-7 - it was light and disposable. You could not throw away a whole RPG-7, but you would not get in trouble for dumping RPG-18 or RPG-22 when in trouble.
In terms of actual use, it was very practical to have couple of these grenades per unit during almost any firefight with the Mujaheddins. If the enemy was using vehicles like Jeeps the grenades could easily damage those beyond the point of practical use. If the enemy was on foot, RPGs could be used to shoot behind the cover so that the rocks and other debris was the shrapnel.
RPG-22 in Afghanistan
Unlike RPG-18, the RPG-22 was not that common during the Soviet-Afghan war. These grenades were developed much later, sometime in the mid-80s, so there were no huge stocks of them at the time. Therefore, they were very limited in Afghanistan, where there was no risk of the enemy tanks present and anti-tank weapons were not in a huge demand anyway.
The RPG-22 itself is an improved version of RPG-18, with a larger warhead which was capable of flying further distance and burning through thicker armor. Being of similar weight to RPG-18 if would have been pretty useful in Afghanistan.
Overall, not the greatest choice for reenactment. If you absolutely must - please only use it for late war impressions. Given that RPG-18 are not common on the collectors market, it is very likely that RPG-22 will be the dominant hand grenade for airsofters and reenactors in the nearest future.
RPG-26 in Afghanistan
There are no good reasons to believe that these were in Afghanistan in any sort of meaningful numbers. Not a good choice for reenactment - aka farb.