French forces landed at Milford Haven in support of Owain Glyn Dwr, 7th August 1405
Owain Glyn Dwr held a claim to the title of Prince of Wales that had not been claimed by a Welshman since the death of Owain Lawgoch in 1378. Owain posed little threat until a dispute involving Owain and the lord of Ruthin was handled unfairly in the eyes of Glyn Dwr.
That, in 1400, sparked a revolt, with Owain being proclaimed Prince of Wales by his supporters, who began attacking English settlements. He rose in popularity and gained support from some English nobles through agreements, the Scots, Castile and the French. By 1405 much of Wales was under the control of Owain or his supporters.
The situation in Wales provided France with an opportunity to pose problems for the Lancastrian regime. It also suited Owain to have the support of men trained in siege warfare. With that in mind, an expeditionary force was dispatched from France to support the Welsh in their operations against the English castles. The support is briefly outlined by Thomas Walsingham:
“In the meantime the French came to the help of the Welshman, Owain Glyn Dwr, and put into Milford Haven with one hundred and fifty ships, having previously lost through lack of fresh water almost all their horses. Lord Thomas Berkeley and Henry Pay burnt fifteen of their ships while they were in harbour. Then the French laid siege to the town of Carmarthen and captured it, having first allowed its defenders to keep all their movable goods, and giving them permission to go wherever they liked. About the same time fourteen other ships were captured by Lord Thomas Berkeley, Sir Thomas Swinburne and Henry Pay while they were sailing towards Wales to help Owain. The steward of France and eight other captains were taken prisoner from aboard these ships.
France’s input into the conflict in Wales was far from decisive. Though it enjoyed some successes, Owain was left with less land under his control at the end of the campaign than he had at the start. Owain attempted to gain further support the following year, asking the Papacy to recognise St. David’s as an archdiocese of the Avignon church which would be in direct conflict with the English backed Roman papacy. France was not stirred into supporting Glyn Dwr again though, and Glyn Dwr’s revolt against the English led to much of the principality being laid waste as he was deprived of supplies by King Henry IV and his son, Prince Henry.