Did the fortunes in the Hundred Years' War depend largely on the weather?

Question

In the Hundred Years' War, the French had more numerous and heavily armed troops, while the English had fewer, more lightly armed (with longbows and less armor) troops that had the advantage of being more mobile.

I am struck by the fact that the most decisive English victories, Crecy, Poitiers, and Agincourt, which were won at heavy numerical odds, were all preceded by rainstorms that hampered the charges of the heavily armored French troops. Conversely, the French won most of the remaining battles, at least those where they had a numerical advantage.

To test my "weather" thesis, I am asking two questions.

1) Did the French ever win any land major battle (not sieges or skirmishes) of one full army against the other, in or immediately after, "bad" (rainy) weather?

2) Did the English ever win any major land battle against the numerical odds (one to two or worse) when the weather was "good" (non-rainy)?

Answer 1

The answer to both questions is yes. To quote specific examples, the French won major battles after "bad", or rainy, weather at the Battle of Saint-Omer and the Battle of Cocherel. The English won the Battle of Auberoche against the numerical odds (5:1 in that case) in good weather.

However, the dataset is probably too small to draw any conclusions as to your main thesis.

The Hundred Years' War actually lasted 116 years (from 1337-1453). Wikipedia lists 56 "major" battles in that time (the list includes sieges and naval engagements!). Ah, Wikipedia!

In my judgement, there were just 17 major battles between "English" and "French" forces in the whole of the Hundred Years' War.

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For what it's worth, my list of major battles would be:

• Battle of Cadsand(): forces approximately evenly matched in terms of numbers. Overwhelming English victory. Weather unknown, but not believed to be a factor.
• Battle of Saint-Omer: English/Flemish force outnumbered French forces 3:1, French victory. Weather had been wet, but was actually irrelevant. The French victory resulted from the superior tactics of the Duke of Burgundy and the Count of Armagnac.
• Battle of Auberoche: French force outnumbered English 5:1, English victory. Weather was fine, but irrelevant. English victory due to superior tactics of the Earl of Derby.
• Battle of St Pol de Léon: French outnumbered English 6:1, English victory. Weather was not a factor.
• Battle of Caen: English force outnumbered French by about 6:1. English victory. French casualties included a large number of civilians killed when the town was captured.
• Battle of Blanchetaque: English slightly outnumbered the French. English victory with heavy French losses. The weather was fine, but was not a factor as the battle was to force a crossing over the Somme.
• Battle of Crécy: French force outnumbered English by at least 2:1 by modern estimates (or far more if you choose to believe contemporary chronicles). Overwhelming English Victory. The weather may have been a contributing factor, but the ground was sufficiently firm to permit repeated charges by French cavalry.
• Battle of Poitiers: French force outnumbered English by at least 2:1 by modern estimates (or far more if you believe contemporary chronicles). Overwhelming English Victory, with the French King John II captured. Wet weather was undoubtedly a factor in the English victory.
• Battle of Cocherel: English forces outnumbered the French by 2:1. Decisive French victory. The weather had previously been wet, but was not a factor in the battle. The result was a victory of superior French tactics.
• Battle of Pontvallain: forces approximately evenly matched in terms of numbers. Overwhelming French victory. Weather wasn't a factor.
• Battle of Agincourt: French force probably outnumbered the English by about 5:1. Overwhelming English victory. Weather was definitely a factor, with rain neutralising the effectiveness of French crossbowmen, and the wet ground hampered the French cavalry charges.
• Battle of Cravant: Franco-Scots forces outnumbered the English by about 2:1. Decisive English victory. Weather was fine.
• Battle of La Brossinière: French outnumbered English forces by about 3:1. French victory. Weather wasn't a significant factor.
• Battle of Verneuil: French outnumbered the English by about 2:1. English victory. The weather leading up to, and on the day of the battle, was apparently fine and sunny.
• Battle of Patay: English forces outnumbered the French by 3:1. French victory. Weather wasn't a factor - the French victory was simply the result of the superior tactics employed by the French commanders.
• Battle of Formigny: forces were approximately evenly matched in terms of numbers. An initial English victory, before the arrival of French reinforcements resulted in a decisive French victory. Weather not a factor, but cannon were employed by the French army.
• Battle of Castillon: forces were approximately evenly matched in terms of numbers, but the French had a significant force of artillery. Overwhelming French victory. Weather irrelevant - French cannon won the day.

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In reality, of course, it is meaningless to talk about the effect of the weather on a battle without considering the topography and underlying geology of the area.

For example, it is often claimed that prior rainfall diminished the effectiveness of the French cavalry at both the battles of Crecy and Agincourt. While this is undoubtedly true at Agincourt, where the rain turned the silty soil into a quagmire, the case is much less clear for the better-drained soils surrounding Crécy. Indeed, accounts of the battles make it clear that, while French cavalry charges became bogged-down in the mud at Agincourt, they were not similarly impeded at Crécy.

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Sources:

• Burne, Lt-Col Alfred H: The Crécy War: A Military History of the Hundred Years War from 1337 to the Peace of Bretigny in 1360, Wordsworth, 1955
• Burne, Lt-Col Alfred H: The Agincourt War: A Military History of the Hundred Years War from 1369 to 1453, Wordsworth, 1956
• Curry, Anne & Hughes, Michael: Arms, Armies and Fortifications in the Hundred Years War, Boydell & Brewer, 1999
• Curry, Anne: The Battle of Agincourt: Sources and Interpretations, Boydell Press, 2000

Answer 2

I think the short answer is: we don't know (yet).

Let me explain why we should stick with this answer until we get the 'accepted answer' from historians.

First, and most obviously, we are speculating and attempting to do historiography as we progress through the list of battles, separating them into whether it rained or not, then check the results of the battles. I'm not sure this would qualify as historical research.

Second, this question is clearly under MilGeo, "Military Geography" (Wikipedia). But, and a BIG but, this is not a well-established topic in the study of history. It can ill-afford weak historical research if it is to get traction with the general population (nor help with the credibility of this site). Hence, even if inadvertently, we will do this area of historical study more harm than good if we were to speculate.

Not a well-established topic: For instance, the Wikipedia link, under section on History and Development of Military Geography, lists a single book to 20th century (1938). In fact, there has been earlier texts from 19th century, such as, T. Miller Macguire's 'Outlines of Military Geography (Cambridge, 1898)' and George Lund Dunnet's 'The Military Geography by an Army Schoolmaster' (Gale & Polden, Brompton Works, Chatham, 1889).

Finally -- on why we should continue to be patient -- since 1994, there has been regular symposiums/conferences all over the world by International Association of Military Geoscientists (this site is hosted by US Navy). Each symposium has a specific theme and, where historical battles are involved, historians do participate. For instance, the one from 2000 (Theme: International Terrain in Military History) resulted in 'Fields of Battle: Terrain in Military History' (Springer, 2002). It did cover some medieval battles, but unfortunately not the Hundred Years' War (the location focus was mainly on the British Isles).

Let me end with a hopeful quote from the editors of Fields of Battle (p.1) (emphasis mine):

Clearly, once a battle is entered into, then all aspects of the terrain may be employee! by astute commanders, and many examples exist where geology, geomorphology or meteorology have combined to defeat an attacker or help a defender. Despite the widespread recognition of the importance of terrain within military action, it has rarely been used as an historical tool to help deconstruct events, actions and outcomes of military engagements, yet clearly its potential to impact our understanding of such actions is considerable. In recent years, however, the relevance of terrain as a tool in the analysis of historical engagements has gained some momentum and it is hoped that this volume will continue this trend.