What have been decisive weapons?

[PanzerJaeger]

The tank and the German tactics associated with it.

[Ramses II CP]

As has been suggested above, you can't isolate weapons from the tactics they required to be successful or decisive. For example you might want to say the change in the length of the Zulu spear was decisive in the rise of that people under Shaka, but without a change in the tactics with which they waged war, a sociological change in the way soldiers were recruited, and far more severe training practices the shorter spear would've been merely a footnote.

You also have to define what you want decisive to mean; decisive in one battle? In one campaign? For one generation? I think some of the most dramatic changes in warfare have come due to relatively minor alterations to current technology, much of it not even weapons. Consider the invention of stirrups, for example. Cavalry operating with stirrups would immediately have a substantial field advantage over cavalry without it... but unless the enemy were utterly eliminated they could carry that idea from the field with them and implement it themselves. The stirrup was exceptionally decisive on any number of battlefields, and perhaps even a few campaigns, but it was quickly and easily adopted by people defeated by it, so it was not overall a world changer.

I can really only think of one weapon whose use was, at least in the minds of the military leaders of the world, so decisive that it changed the nature of fighting war itself. The obvious, nuclear weapons. I think Korea, Vietnam, and Afganistan are clear demonstrations that the same essential tensions which caused the first two world wars would've caused more of the same in the absence of the fear, whether justified or not, surrounding the nuclear weapon.

I accept, however, that this may be a limitation of the fact that I'm alive right now rather than alive right after WWI when I might've thought the same of chemical weapons or machine guns.

[The Wizard]

None of those mentioned in the OP were warfare-changing weaponry and therefore don't fit the bill.

I'd say the most influential are the repeating rifle and the machine gun, which gave European (Western) armies their first and only decisive technological advantage over their non-Western rivals, and for a short time (approximately two to three decades) gave them an unparalleled ability at war. That this period coincides with the Scramble for Africa is no surprise.

A trailing third, after those two tied at first, I'd say would be the airplane. And maybe, just maybe, the tank for fourth place.

[Fragony]

None of those mentioned in the OP were warfare-changing weaponry and therefore don't fit the bill.

In the case of the longbow and goedendag, ok, but the bayonette? You kidding me it was a revolution in warfare, it make a charge dangerous because of the firepower, and it made shields useless because of the side-stab (attacking the guy the guy next to you is fighting) and has stayed the dominant weapon on the battlefield for decades to come and it's still used even today, probably the most revolutionary weapon out of all of them.

[The Wizard]

The bayonette did change warfare, but not decisively. Before the advent of repeat-action rifles and machine guns, no manner of sophistication in weaponry meant anything on a strategical scale, and therefore organization, tactics and strategy were key (see, for instance, the result of the introduction of European style warfare in India; the British didn't conquer the place 'cause they had better guns, but because they were better organized). And after the diffusion of said technology (i.e. when everybody had machine guns) around 1900, it returned to that.

Oh, I forgot one more crucial innovation in warfare that decisively changed things worldwide: the bright European idea of putting guns on (big) ships. While it took them until the 19th century to achieve a decisive technological advantage on land, at sea Europe had been far ahead militarily since the 15th.

[Fragony]

I'd say the bayonette was a bigger departure from the old ways then the machine-gun, see WW1 which was the old (bayonette) way of fighting a new war, didn't so much change tactics just the amount of deaths, while the bayonette instantly made the old ways absolete making the brittish unbeatable untill others adapted.

[Rhyfelwyr]

Well the tactics Cumberland used with the Bayonet where each man protected the one to his right were limited in their usage. Plus, it required a lot of discipline for the troops to hope the man to their left would protect them. Despite the boggy ground hampering the Jacobite charge, the Hannoverian right flank still very nearly broke at Culloden. Thankfully it didn't.

[Fragony]

Well the tactics Cumberland used with the Bayonet where each man protected the one to his right were limited in their usage. Plus, it required a lot of discipline for the troops to hope the man to their left would protect them. Despite the boggy ground hampering the Jacobite charge, the Hannoverian right flank still very nearly broke at Culloden. Thankfully it didn't.

Well yes but that is because other nations adaptod the bayonette later on, it really is an end of an era that just can't be denied.

[The Wizard]

I'd say the bayonette was a bigger departure from the old ways then the machine-gun, see WW1 which was the old (bayonette) way of fighting a new war, didn't so much change tactics just the amount of deaths, while the bayonette instantly made the old ways absolete making the brittish unbeatable untill others adapted.

The bayonet did not give European armies the ability to conquer vast swaths of land with minimal forces. The machine gun did. The time when the machine gun and the repeating, bolt-action rifle were only available to European forces was probably the only time in history where tactics and strategy didn't matter. Once the opposing forces gained the technology, of course, that advantage rapidly disappeared (like in the Rif War, for instance).

Nor have I heard of the British being the first to use bayonets. As far as I know it was the French, and the idea was rapidly adopted by all major European powers in turn, making it widespread by the 1660s.

There had been projectile weapons on ships before that, and people had been experimenting in trying to fit as many and as big guns as they could on deck.

Not on the scope and scale that early modern Europeans did it, nor with the same reach and mobility, nor with the same firepower. European naval power allowed them to usurp world sea trade by the 17th century, long before they became economically dominant following the Industrial Revolution.

P.S. Army B would win. Army A cannot sustain a war effort on the same level that Army B can. Take the conquest of the Americas by the Spanish as example -- had disease not crippled indigenous society and had internal conflict not been properly exploited by the Spaniards, there would have been none.

[Fragony]

Yeah I guess you are right, indeed isn't as significant as the machine gun and, and it is a bit much to call it tactics it was more like a massacre.

[Kraxis]

Nor have I heard of the British being the first to use bayonets. As far as I know it was the French, and the idea was rapidly adopted by all major European powers in turn, making it widespread by the 1660s.

True the French were the first to use it, but it was a very different weapon to the British, or should we call it the 'modern' bayonet (the really modern one is basically just a long knife) as I don't think the British actually invented it, but merely adopted it.

The French, initial, bayonet was a simple on the spot device. It was a blade with a handle you put into the barrel of the gun. Obviously that presented certain problems for the user, such as when is it prudent to use it, how can I shoot with it in place etc. The modern bayonet removed such problems and gave the user a readily useable short range defensive weapon, which later became a highly offensive weapon as tactics developed.

The modern bayonet was a quantum leap in effectiveness over the old French bayonet. But indeed it was hardly as important as the MG or repeating rifle.

I will personally say the machinegun, though the howitzer certainly does make a powerful case, being the most deadly weapon ever (it has the highest single toll of human life from human generated means, with about 60% of WWI casualties and another 40% from WWII), and it has only existed for around 150 years. Though the precursor, the bombard, is pretty old.

[Pannonian]

Oh, I forgot one more crucial innovation in warfare that decisively changed things worldwide: the bright European idea of putting guns on (big) ships. While it took them until the 19th century to achieve a decisive technological advantage on land, at sea Europe had been far ahead militarily since the 15th.

There had been projectile weapons on ships before that, and people had been experimenting in trying to fit as many and as big guns as they could on deck. However, naval-wise, I'd nominate the Brit who had the bright idea of putting a plane on a ship. By putting those two arms together, the idea of the fighting ship became obsolete.

Other landmarks:
Developing the cavalry mount - armies became that much more mobile and long-range, especially those who relied most heavily on horse.
Tinned food - states could now prepare long, long in advance for long, long campaigns.
Internal combustion engine - armies and navies were no longer dependent on organic transport or windpower, but on fuel that was easily stockpiled.

Army A has modern personal weapons, but is limited to horse transport, and specifically pre-cavalry horse, and traditional methods of feeding the army. Army B is armed with pre-gunpowder weapons, but has access to stockpiled supplies and modern transport, assumed to be lavishly supplied with fuel. Neither army can use the other's resources. Who would win?

[Rhyfelwyr]

There had been projectile weapons on ships before that, and people had been experimenting in trying to fit as many and as big guns as they could on deck. However, naval-wise, I'd nominate the Brit who had the bright idea of putting a plane on a ship. By putting those two arms together, the idea of the fighting ship became obsolete.

Other landmarks:
Developing the cavalry mount - armies became that much more mobile and long-range, especially those who relied most heavily on horse.
Tinned food - states could now prepare long, long in advance for long, long campaigns.
Internal combustion engine - armies and navies were no longer dependent on organic transport or windpower, but on fuel that was easily stockpiled.

Army A has modern personal weapons, but is limited to horse transport, and specifically pre-cavalry horse, and traditional methods of feeding the army. Army B is armed with pre-gunpowder weapons, but has access to stockpiled supplies and modern transport, assumed to be lavishly supplied with fuel. Neither army can use the other's resources. Who would win?

If it was on the defensive, Army A would win. Of course a large-scale offensive for army A would be almost impossible.

[KrooK]

Weapons that allows victories even when army which used them commited so many mistakes that normal it would loose in any conditions.

1. Charrior
2. Greek phalanx
3. Roman pilum
4. Crossbow
5. Gunpowder
6. Hussaria lance
7. Bayonett
8. Improved missile weapon
9. Plane
10. Tank
11. Nukes

[Mangudai]

The tank and the German tactics associated with it.

Yeah... I think the German victory over France was half genius and half luck. The French (and BEF) played perfectly into German hands. The allies could have stopped the blitz if they deployed more intelligently.

[Sabuti]

The first club! Me smash head with stick, me win.

[TinCow]

Off the top of my head and in no particular order:

Recurve Bow
Tank
Flint-lock Muskets
Rifled Barrels (as differented from smooth-bore)
Repeating Rifle
Machineguns
Aircraft
Ironclads
HMS Dreadnought
Aircraft Carriers
Corvus

[Mangudai]

Off the top of my head and in no particular order:

Recurve Bow
Tank
Flint-lock Muskets
Rifled Barrels (as differented from smooth-bore)
Repeating Rifle
Machineguns
Aircraft
Ironclads
HMS Dreadnought
Aircraft Carriers
Corvus

I'd take Flint-lock Muskets, Rifled Barrels, and Aircraft off the list. While these all became important eventually, they were not game changers right off the bat. The flint-lock was about equal to the matchlock except less prone to accidents. The rifle didn't truly trounce the smoothbore until about 100 years after its debut. Because smoothbores reloaded faster (looser fit) and could use buck and ball. Aircraft were not a game changer in WWI.

I would add breach loading rifles. An early example is Abel Straights Lightning Mules Brigade, which trounced vastly superior numbers in Georgia. The Germans soon improved their doctrine by training soldiers to fight on their bellies. They absolutely crushed their opponents in the Franco-Prussian war.

[Kekvit Irae]

For me, a favorite would be the British Mark 1.
It wasn't very decisive on the battlefield, but just the very invention and deployment of the weapon revolutionized combat for the next hundred years, most notably in 1939.

[Ja'chyra]

Clovis spearpoints
The Bow
Iron
Horses
The Gladius
Gunpowder
The rocket
Aircraft
Tanks
Chemical, Biological and nuclear weapons

Although all of these can be worked around with the right tactics. Almost all weapons could be considered to be decisive in some sense of the word but it really depends on how they were used and who by, there'd be no point giving a nuclear bomb to a stone age man. But I think the main thing is how they were used.