The Arquebus was a type of firearm that was commonly used between the 14th and 17th century. It was a type of matchlock, the barrel was generally a smoothbore (i.e. it had no rifling) and it was loaded from the muzzle end (i.e. a muzzle-loader). The user was called an Arquebusier or a Harquebusier. The word is derived from Dutch Harkbuss which means a Hook-gun.
The Arquebus was first employed by the Chinese towards the middle of the 14th century and by early 1500, they had spread to Europe and were being used by Hungarian troops. Images of arquebusiers can be found in Rembrandt's famous painting titled The Night Watch.
Most early arquebusiers were usually knowledgeable about the construction of their weapon. Quite a few of them were the actual makers of their own weapons as well. The weapons weren't known for their accuracy, given the smoothbore barrel and primitive sights. A crossbowman or longbowman could fire with greater accuracy and range. However, firing a crossbow or longbow took literally years of practice to become proficient with the weapon, whereas an arquebus could be mastered by anyone in a lot less time. Once people had mastered the art of producing gunpowder and shot, it was easier to mass produce ammunition for an arquebus as well, whereas fletching (the art of making arrows) was still a craft that needed highly skilled labor to produce.
On the other hand, an arquebus was vulnerable to heavy fog and rain, since the user needed to keep his slow match lit. This is a problem with all matchlocks, as the article on matchlocks indicates. There was also a danger that the sparks from one person's arquebus could set fire to the powder supply of the person next to him. Unlike a longbowman, an arquebusier was generally helpless after his shot was fired and his weapon was heavier to carry, so it was not surprising that the bow was considered a superior weapon for many years.
To compensate for the arquebus's weaknesses, some strategies were evolved. For one, an arquebusier was sometimes accompanied by an assistant called a varlet, whose job was to help the arquebusier carry all his gear and keep a fire going. Since reloading took some time, tactics involved placing the arquebusiers in lines of three, so that when one line was done shooting, they could move to the back and reload, while the next two lines fired a volley each. Arquebusiers were also equipped with a sword as a second line of defence, if they couldn't reload in time. In order to compensate for inaccuracies of the weapon, commanders would line up several men next to each other and order them to shoot at the same time, in the hopes that at least some of them would hit the enemy troops.