The first bayonets plugged the barrel, so muskets could not fire
Early bayonets simply jammed into the muzzle of a musket, turning it into a spear but making it impossible to shoot. Soldiers had to wait until the last moment to fix them. At Killiecrankie in 1689, Highlanders exploited that delay, charging before their opponents could get their blades in place.
The first clear record of a true bayonet comes not from Europe but from a Chinese military treatise, the Binglu, published in 1606. It describes a gun-knife, a short blade about 57.6 centimetres long that slotted into the barrel of a breech-loading musket and locked with a twist, giving a combined length of 1.92 metres. Soldiers were told to fit it when powder and shot ran out or when enemies came too close to reload.
In Europe, French troops reportedly used crude foot-long plug bayonets during the Thirty Years' War, and General Jean Martinet standardised them for new French fusilier regiments in 1671. After Killiecrankie, the defeated commander Hugh Mackay is believed to have devised a socket bayonet, which clipped around the outside of the barrel with an offset blade so the musket could still be fired and reloaded.
Adoption was bumpy. Louis XIV rejected an early socket design in 1690 because it tended to fall off. The English and Germans abandoned the pike for socket bayonets shortly after 1697, but Britain's triangular spike had no lock and was notorious for dropping off in battle. The French solved that in 1703 with a spring-loaded catch, and by the mid-18th century most European armies used sockets. Longer sword bayonets then appeared, helping shorter rifles match the reach of muskets when forming squares against cavalry.
The name is murky. It is often traced to Bayonne in southwestern France, but the town had no notable knife industry, and the link seems to owe much to Voltaire's 1723 poem La Henriade. Today most armed forces see bayonets as a last resort, though they still appear at parades and serve as utility knives.
Source: Bayonet
