How did flamethrowers affect WWII and how were they were used?

Flamethrowers were used in WWII mainly by the United States, and mainly in the Pacific.  This is because flamethrowers were mostly useful for attacking strong points like pill boxes in prepared defensive positions.  Their range and the amount of time for which they could be used were both too short to make them useful for other purposes.  They affected WWII mainly by making it somewhat easier (though by no means easy) for American forces to defeat the Japanese on various islands in the Pacific.

The US military did not use flamethrowers in WWI.  Therefore, they did not have a good flamethrower ready by the time WWII started.  Early models did not work well and it was not until 1943 that flamethrowers were used much by the US.  When the US did use them, it was mainly in the Pacific.  There, the US had to invade island after island held by the Japanese.  The Japanese had had time to fortify the islands and had numerous concrete emplacements from which they could fire at US troops.  These emplacements were very hard to defeat.

The flamethrower was used to defeat them because it could reliably fire its flames through the small apertures in the emplacements.  When the flames went through, they would fill the emplacement, killing or wounding everyone inside.  This would not be possible with bullets, which would have a harder time entering the emplacement and would then only go in a straight line.  Therefore, flamethrowers were used against these emplacements.  They had to be supported by infantry because a flamethrower could only throw its flame about 40 yards at the farthest and because they only had less than 10 seconds’ worth of fuel.  This meant that flamethrower operators and support people had to be protected at all times because they would be defenseless much of the time.

The flamethrower was important in WWII because it helped the US crack the defenses of these islands that Japan held.  The flamethrower alone could not make it easy to defeat the Japanese defenses because of its limitations, but it was very useful in certain situations. Without it, the US would have suffered even more casualties than it did.  Thus, this weapon did not determine the outcome of the war, but it reduced casualties on the American side.