I was referring to rifle-attached grenade launchers or RPGs as anti-personnel weapons. How did they affect tactics or warfare in general?
Rifle mounted grenade launchers have been around for awhile - they first came into widespread usage by the US in the 1970s with the M203. The M203 replaed the stand alone M79 (which fired the same 40mm round), which in turn had replaced rifle-grenades in the early 1960s. Both the M79 and M203 were designed to perform the same role that rifle grenades had been filling since WW1 - which was to provide the infantry squad with a light weight HE projectile capability between the hand grendade and the mortar. This role was also filled by such weapons as the British 2" 'Commando' Mortar and the Japanese 50mm Grenade Projector (a.k.a. 'Knee Mortar').
All of these weapon systems give the infantry squad the ability to fire a small HE projectile, directly or indirectly, at much greater ranges than was possible with the hand grenade.
The modern grenade launcher's advantage over rifle grenades is greater effective range and accuracy. The projectiles are also smaller and less cumbersome, allowing the grenadier to carry more ammunition. Finally the rifle mounted GL doesn't interfere with the firing of the rifle the way a rifle-grenade does when it is a loaded.
Rifle-grenades do have a couple of advantages themselves - they can be much larger (not being limited to the diameter of the GL barrel) which means they can be more powerful (bigger HE charge), as well as have a much better AT capabilty (the greater the diameter of the shape charge, the more armor penetration).
The RPG was primarily intended as a light anit-tank weapons with a secondary AP role (Russian RPGs have HE-FRAG and Thermobaric rounds as well as HEAT). They have comparable effective ranges to grenade launchers and rifle grenades, but are much larger and bulkier and lack any indirect fire capability. RPGs are also notoriusly inaccurate, especially at longer ranges. The larger round (85mm for RPG-7) does give them a much better AT capability and for the HE-FRAG rounds, a much larger casulty radius over 30-40mm GL rounds.
How are they all used?
US doctrine puts 1 40mm under-barrell M203 or M320 GL in every 4-man Fire Team.
In some organizations the GL is carried by the team leader, in others by a dedicated grenadier. SOPs vary.
The GL is used to engage enemy targets behind cover, in defilade, inside of buildings. It is also used to cover deadspace and to fire smoke for marking. It is an excellent weapon for urban enviorments, giving the infantry the ability to accurately enagage targets in upper story windows and rooftops. In the past this would have been done less effectively with rifle-grenades or hand grenades.
The US equivilent to RPGs - the M136 AT-4, the M141 BDM (aka SMAW-D), the M72, and the Mk 153 SMAW (all rocket launchers) - are used in the current operating enviorment primarily to engage enemies behind cover, in buildings or caves, or in vehicles. All of these weapons, except the Mk 153, are single shot "disposable" weapons. The AT-4 and M72 were designed primarily to enage AFVs. The M141 is primairly a bunker buster, and the Mk 153 can fire both HEDP and HEAT rockets.
The RPG is a very popular weapon with all kinds of unconvential combatants (insurgents, militias, rebels, terrorists, etc.) becuase they are cheap , simple and everywhere. They tend to be the heaviest direct fire weapons these kinds of forces have access to, and are as a result are used for everything . They give unconventional forces a credible short ranged anti-armor capabilty (especially in close terrain like cities or mountains), when massed or volley fired act as a kind of pocket artillerty - great for initiaitng ambushes.
The RPG (along with the mortar) is the poor man's artillery.
On potential game changer is the new US XM25 Counter Defilade Target Engagement (CDTE) System. The XM25 is a 25mm semi-automatic, magazine fed GL that uses an advanced sights and a targeting system to accuratelty fire electonically fused 25mm airbursting greandes out to nearly 800m. They are being field tested in Afghanistan and have proven to be devestatingly lethal against the Taleban. The airburst feature detonates the grenade ~1m above the target, rendering traditional cover (i.e. hiding behind a rock or wall) ineffective.
Adrian