Are there any major differences between the two weapons? Did the English further developed the longbow when they took it from the Welsh to make it their own or is this another case of England 'stealing' another invention?
I'm debating with someone and their argument is that the Welsh had their version of the longbow first and that Welsh archer were used in English campaigns, so the English didn't really developed anything other than incorporating the tactics into their strategy.
The first point to make is that the longbow was not 'invented' in the Middle Ages. The first know example of a self bow (that is, a bow made from a single piece of wood) long enough to be considered a 'longbow' is a Neolithic artefact from the Ötztal Alps. The first longbow found in Britain, the Meare Heath bow, is also Neolithic. Both of these bows were made from yew, like the archetypal medieval Anglo-Welsh weapon. However, the latter is not descended from a Neolithic type. In fact, a lack of arrowheads suggests that bows were uncommon in Britain during the Iron Age. 40 yew longbows, in this case dating to the fourth century AD, have been found at Nydam in Denmark. The Ötztal bow was found frozen in ice, while the Meare Heath bow and the Nydam bows were preserved in peat bogs, thought to have been deposited as religious offerings. With changes in religious practice, people ceased throwing bows into bogs, and thus later examples have mostly rotted away. We have plenty of examples of sixteenth-century English longbows, from the underwater wreck of the Mary Rose, but no medieval examples. In fact, before the discovery of the Mary Rose in 1971, historians tended to estimate that longbows were a bit shorter than the Mary Rose examples indicate.
You might think that contemporary written sources would tell us how long contemporary bows were, or even if the Welsh were using longer bows than the English at one point. Unfortunately, medieval records tend not to be very descriptive of simple weapons such as the bow. Such items were commonplace, and it was assumed that the audience would be aware of what they were like. Moreover, medieval authors were primarily devoted to legal, religious, and political matters. The people who actually used bows were mostly illiterate, and those archers who could write had better things to do than write treatises on basic hunting equipment. Another difficulty is that 'longbow' is a modern categorisation, not a medieval term. People didn't suddenly start calling self bows longbows when they got longer. There are late medieval uses of the word 'longbow', but it is unclear as to whether this was to differentiate them from shorter self bows, or from crossbows. In fact, Matthew Strickland and Robert Hardy argued, in their 2005 book The Great Warbow, that English bows had always been longbows. After all, earlier peoples were certainly capable of making longbows, and there are no surviving early medieval bows to prove that bows of this time were shorter. Other scholars, such as Clifford Rodgers, have argued that medieval iconography, such as that of the Bayeux Tapestry, indicates that high medieval bows were shorter than those depicted in the fourteenth century.
To finally get on to Wales, where does the idea that the Welsh invented the longbow come from? With regard to this period of history, sources from and about Wales are fairly rare. Thankfully, the monk Gerald de Barri (now known as Gerald of Wales) both travelled and wrote extensively about the country. In one account, he describes archery in South Wales:
'It seems worthy of remark, that the people of what is called Venta 2 are more accustomed to war, more famous for valour, and more expert in archery, than those of any other part of Wales. The following examples prove the truth of this assertion. In the last capture of the afore-said castle, which happened in our days, two soldiers passing over a bridge to take refuge in a tower built on a mound of earth, the Welsh, taking them in the rear, penetrated with their arrows the oaken portal of the tower, which was four fingers thick ; in memory of which circumstance, the arrows were preserved in the gate. William de Braose also testifies that one of his soldiers, in a conflict with the Welsh, was wounded by an arrow, which passed through his thigh and the armour with which it was cased on both sides, and, through that part of the saddle which is called the alva, mortally wounded the horse. Another soldier had his hip, equally sheathed in armour, penetrated by an arrow quite to the saddle, and on turning his horse round, received a similar wound on the opposite hip, which fixed him on both sides of his seat. What more could be expected from a ballista?'
Gerald was certainly describing unusually powerful bows, whether or not the stories he had heard were true. However, he goes on to say:
'Yet the bows used by this people are not made of horn, ivory, or yew, but of wild elm; unpolished, rude, and uncouth, but stout; not calculated to shoot an arrow to a great distance, but to inflict very severe wounds in close fight.
That these bows were made of elm, and not yew, tells us that they were not the direct ancestors of the archetypal Anglo-Welsh warbow. Gerald's claim that they did not have great range also suggests that they were rather different from later longbows. This impression that the South Welsh bows were stout and short is backed-up by a thirteenth-century woodcut of a Welsh archer, which shows a fairly thick and rather short bow. Individual illustrations from this period are not always very realistic, but it does fit with Gerald's account.
It is sometimes argued that, since Edward I's armies in the Welsh wars and in his Scottish wars included large numbers of archers, that the use of massed archery was a Welsh influence. However, laws designed to recruit large numbers of English archers go back decades before, with the 1252 Assize of Arms stipulating that free men of middling means should serve the King as archers. This is in contrast to the 1181 Assize of Arms, which mentions only men to be equipped as cavalry and spearmen. Nonetheless, archers had certainly been recruited in large numbers in England, as is attested by Ailred of Rievaulx's account of the Battle of the Standard, fought in 1138. Despite this, we cannot say that English archery was not inspired by the Welsh. Indeed, it would make sense that warfare in a country as poor and hilly as Wales might involve a lot of archery, and our earliest figures for large numbers of archers in English armies do come from Edward I's campaigns. There are, however, plenty of other explanations for this other than a particularly Welsh use of the longbow or massed archery. In short, there is no evidence which firmly suggests or precludes that the archetypal longbow was a Welsh invention.