I often hear stories of flamethrower troops storming the beaches of Iwo Jima and burning bunkers full of troops.
But isn't it more risky to carry a tank of flammable liquid with limited fuel and range when chucking a few grenades into a bunker could suffice? Wouldn't you just become a bigger target for the enemy?
Flamethrowers can be useful for the assault on field fortifications:
Flamethrowers are less effective as a general-purpose infantry weapon:
Basic flame weapons are effective against flammable targets or in very close quarters. Normally they are not used in any situation where the defenders would have a clear view of the attackers. Flame weapons are currently popular among insurgent fighters due to their simple operation and effectiveness in ambush situations.
In World War II, flame throwers were used to clear out no-surrender fortified positions which were primarily found in the Pacific theater of war. Normally when a line or position is overrun the defenders will retreat or surrender. This was not the case for Japanese forces which would often hole up in pillboxes or bunkers and fight to the end. Against such positions a flame thrower is effective if the attacker can approach it from the side or the rear and incinerate it. When the defensive line is intact this is not usually possible, so flame throwers were primarily used in "mop up" operations to destroy fortifications that had already been strategically nullified.
In modern warfare, flame throwers are considered to be largely superseded by thermobaric weapons or incendiary rockets which are more powerful and work at longer ranges. Thermobaric weapons are useful in urban or other close quarters in which it is either (1) difficult to target projectile weapons, or (2) the situation is so close, that the use of projectile weapons could harm friendly forces accidentally.
The US equivalent is the Flash rocket launcher. American forces rarely use the Flash due to the high probability of civilian casualties if the weapon is used in an urban environment. Modern military soldiers also have access to incendiary grenades which can be used to ignite flammable materials. These weapons can be effective against pillboxes or other positions which have a limited field of view. Normally such positions are no longer tactically relevant because modern artillery and rockets are so accurate and powerful that pillboxes can be destroyed from a long range.
Flamethrowers are good for "close" fighting. Their disadvantage is that they can only be used at closer range than is usually the case for most other weapons.
In a normal combat operation, an enemy position will be reduced by shell and/or rifle fire to the point where there are few defenders. Usually, that was enough; the remaining defenders would either surrender or retreat, and in either event, the position would be carried.
Not so the Japanese. They would fight to the last man, which meant that the Americans had to kill them to the last man. Flamethrowers were good for this purpose because the flames, or at least the smoke, could permeate small holes that artillery, bullets, and even grenades could not, thereby killing with either fire or aphyxiation.
The dangers of using flamethrowers were lessened when there were few, isolated defenders, but not eliminated. A soldier hit in normal combat might have a chance of surviving; the carrier of a flamethrower would almost certainly die if his gas tank were hit, or he were hit in a way that caused him to lose control of his weapon. Plus, he would have to approach so close to use his weapon that an enemy that could get a shot at him would be firing at almost point blank range.
