The star that falls from Heaven is Apollyon, who governs the bottomless pit.  He opens the gates to warfare, but the war is a restricted one, "And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them" (Revelation 9:6)  This restricted war occurs for two reasons.  First, a select number of individuals finally understand and believe what they were told repeatedly about prayer, and so they pray the Prayer for God's Justice as well as others which enable them to perform miracles "And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth. These are the two olive trees, and the two candlesticks standing before the God of the earth. And if any man will hurt them, fire proceedeth out of their mouth, and devoureth their enemies: and if any man will hurt them, he must in this manner be killed. These have power to shut heaven, that it rain not in the days of their prophecy: and have power over waters to turn them to blood, and to smite the earth with all plagues, as often as they will" (Revelation 11:3-6). Secondly, those with military power seize upon the realization that they may attack with impunity, if their cause is just "And it was commanded them (the 'locusts') that they should not hurt the grass of the earth, neither any green thing, neither any tree; but only those men which have not the seal of God in their foreheads" (Revelation 9:4). They boldly attack, and a number of them meet with success, but only for a limited time "And to them (the 'locusts') it was given that they should not kill them (those without God's seal), but that they should be tormented five months" (Revelation 9:5).

The locusts, as is clear from their description, are no ordinary locusts.  They are war machines as is made clear by "The shapes of the locusts were like unto horses prepared unto battle" (Revelations 9:7) and "They had breastplates, as it were breastplates of iron; and the sound of their wings was as the sound of chariots of many horses running to battle" (Revelations 9:9). This combination of descriptive items suggests camouflaged military helicopters. We can not expect St. John to have understood what he was seeing (see my discussion on Prophecy), so his description must be interpreted:

• The helicopters are called  "locusts", because they have a body shape like locusts, they fly erratically, the fly in packs, and they can land and take off in fields. This is also a good indication that the helicopters are painted military green or camouflaged.
• They kick up dust as they fly and give off smoke as they shoot, and their targets explode and give off smoke, "and there arose a smoke out of the pit, as the smoke of a great furnace; and the sun and the air were darkened by reason of the smoke of the pit. And there came out of the smoke locusts upon the earth" (Revelation 9:2-3).
• Their armor is indicated by their "breastplates of iron" (Revelation 9:9).
• The pilot in the front window is indicated by "their faces were as the faces of men" (Revelation 9:7).
• The great roar of the engines and rotating blades is indicated by " the sound of their wings was as the sound of chariots of many horses running to battle" (Revelation 9:9).
• The whirling blades are indicated by "they had hair as the hair of women" (Revelation 9:8).
• A helicopter's tail goes straight out and then has a vertical tail fin,  "they had tails like unto scorpions" (Revelation 9:10).
• They are equipped with guns and missiles "and there were stings in their tails" (Revelation 9:10).
• The rotor rods or blade supports are highlighted with gold "on their heads were as it were crowns like gold" (Revelation 9:7).
• As is typical for military craft, the 'face' of the helicopters is painted with a ferocious jaw, "their teeth were as the teeth of lions" (Revelation 9:8).

The number "five months" is not necessarily meant literally. Words like 'month' and 'day' are used in Revelation to refer to a cycle of time, an episode, not to a fixed unit of time. For example, a horse race is an episode, but not all races last for the same amount of time. In this case, it is likely that the period 'month' refers to about a decade, so a period of about 50 years is indicated.  Helicopters first began to be used in warfare in the Korean War, which started in June, 1950. The injunction that "And to them (the 'locusts') it was given that they should not kill them (those without God's seal)," refers to the fact that the helicopters were also used to save lives.  And the remark, "And in those days shall men seek death, and shall not find it; and shall desire to die, and death shall flee from them" points to the remarkable progress made by medicine which rendered many types of wounds, which in earlier times would have been deadly, non-fatal.