Its not correct to say that human wave was rendered obsolete during ww1.

Unsupported infantry bayonet charges against prepared trench works were rendered obsolete, but by the end of the war only the method of artillery preparation, the armament of the infantryman, and the tactic of feeding men into breakthrough sectors while encircling holdout positions had changed.

The stormtroopers, while representing the first real breakthrough in offensive technology together with the tank, still attacked in human wave.

Fast forward to ww2, and now we have the birth of modern infantry tactics. Using a fire and flank team in unison to suppress and eliminate defensive positions was indeed a huge step forward in putting an end to hundreds of men charging over a field to bayonet a defender to death.

However, such tactics don't work when the density of troops is high. If, as in ww1, there is no way to flank an enemy because no flank exists, human wave was still the only way to push ahead without armor.

The soviet army was a HUGE user of human wave tactics right up until the battle of Seelow Heights at the end of the war. The infantry now had submachine guns instead of rifles, the artillery was much more accurate, and tanks often supported the assault, but the basic idea was still the same.

In the slow allied advance up the Italian peninsula, the same thing happened. The concentration of men was so high, there was no way to advance but to charge.

In the desert campaign, tanks were the emperors of combat, but the infantry still had to charge in human wave in support of those tanks.

In river crossings, human wave was the ONLY tactic against an entrenched enemy.

The only exception was when artillery was available to provide smoke to cover the advance, but this was not always possible. The russians also experimented with blinding searchlights in nighttime assaults, but with poor outcomes.

In the eastasian theater, the japanese initially used human wave tactics very effectively, but in the end suffered greatly because unlike the russians, they lacked the heavy fire support, armor support, and firepower per infantryman that submachineguns provided.

So, by the time the war you're talking about came around, the only thing that had really changed was that infantry usually performed the hu,an wave in concert with tanks, gumships, and heavy fire support.

The iranian army was able to achieve some success without all of these by using overwhelming numbers alone. Their high morale broke some iraqi unit's will to fight, and many MG positions simply ran out of ammo.

So imagine you are an iraqi soldier. You and about six of your buddies are holding a position when you see fifty iranian troops charging at you. They are coming fast. You shoot, you miss, you shoot again, some die, but you become acutely aware that they are getting closer, they don't seem to be stopping, and god knows what's happening on your flanks. What if they've overrun the position to your left? You panic. you lookaround, and you see fear in the eyes of your squad. You abandon your MG and get the hell out of there while the going is good.

Thats how human wave works.

It's easy and fun to think human wave attacks are a pre-machine gun thing but one of the most remembered feats of the 2nd world war was probably the storming of Omaha Beach on D day.

Here's the armament left on the beach after the bombardment failed to hurt even a single German soldier:

That beach was covered by 8 bunkers with large guns, 35 fortified smaller bunkers with smaller guns, 85 machine gun nests, 4 artillery batteries, 18 anti-tank guns, 6 mortar emplacements and 35 rocket launching sites with 4 rocket launchers each.

So the soldiers storming that beach stormed against that, unsupported by artillery and with no armor to speak off. And they made it.

I'd love to see a statistic or some research on the waning effectiveness of human wave attacks. But as an anecdote D day should point out that human wave attacks were not decisively repulsed every time.

Human wave attacks weren't decisively repulsed in both World Wars. In fact, the employment of human wave attacks is tied in with its effectiveness and the context of the battle being fought.

In WW1, when mobility was constricted and high numbers of troops were concentrated, fire and maneuver tactics and mobility didn't exist, attacks still relied on human wave elements - though more sophisticated at war's end (e.g. stormtroopers).

In WW2, when the battlefield provided much more mobility (via airborne and mechanized infantry) and troops were spread out over larger areas, human waves weren't as common. That being said, they still very much existed in WW2 - a beach assault against a fortified enemy such as Normandy or Tarawa is very much a human wave assault.

The difference for why they succeeded far more in WW2 than in WW1 was that there weren't as many troops concentrated in the battlefield and hence breakthroughs couldn't be stopped as easily as in WW1 when you'd have a lot of troops available in reserve. Likewise, the ability to coordinate firepower and heavy support weaponry (tanks, mobile artillery pieces, etc.) for infantry made the attacks much more effective.

Of course, the Korean War saw a return of human wave attacks, primarily by the Chinese. Again, look at Korea - you are in a constricted peninsula so there is little room for flanking. The terrain is extremely mountainous and so armor and airborne infantry aren't effective (and the advent of helicopter assault wasn't available yet). What ended up happening was a return to WW1 style static line warfare, in which case the human wave returned.

As for Iran-Iraq, its similar in that there was a lack of mobility (lack of armor and aircraft to enable a mobile warfare) but plenty of infantry with small arms. With little in combined arms training or support, the war eventually became one of static-lines where human waves were the only way to breakthrough.