Historians studying the period of baronial reform and rebellion between 1258 and 1267 have overwhelmingly concentrated upon the conventional (land-based) campaigns of Lewes and Evesham. Others have focused on the protracted siege of Kenilworth Castle in 1266. Surprisingly little attention has been paid by scholars to naval matters in this crucial decade in English history. Instead they have mainly viewed the maritime theatre of war as little more than a sideshow. F.W. Brooks, for instance, noted that the ‘naval side was subordinated to the military’, while N.A.M. Rodger devotes just a single paragraph to nautical aspects of the Barons’ War in his classic study, The Safeguard of the Sea.Yet throughout this period the waters surrounding the British Isles, in particular the English Channel, were the scene of constant naval activity. This essay will examine the maritime theatre from the baronial reform movement's genesis in April 1258 through to the formal ending of hostilities in July 1267, arguing that it was far more significant than has been previously recognised. Emphasising the importance of maritime security and control to both royalist and Montfortian strategic planning, it will also discuss how naval affairs directly impacted on the land-based campaigns.

In the twelfth century the English Channel had formed the backbone of the transmarine Angevin Empire, the disparate assemblage of territories under Plantagenet rule that stretched from the Cheviots to the Pyrenees. Transfretation was commonplace as courtiers, administrators, envoys, messengers, troops and merchants crossed the English Channel either on official business or to pursue their personal affairs at the peripatetic royal court. Sea routes from Channel ports such as Southampton and Winchelsea, which collectively formed the northern axis of an extensive maritime trading zone, extended as far south as Bayonne in Gascony. These transmarine lines of communication and commerce, vitally important for the empire's governance and economic stability, were strategically secure: both sides of the Channel, as well as the sea coasts of Brittany and Aquitaine, either lay within Angevin lordship or under the control of Continental allies. Naval operations in these waters were therefore mainly logistical exercises involving the transportation of men and materiel.