The feudal army was summoned for the last time in the 100 year war with France, which began in 1337. In it the English longbow was used to pierce French knights' armor. Guns and cannon with gunpowder were introduced in 1338. They became common by 1372 and foresaw the end to the competition between the strength of arrows to pierce and the heaviness of armor to resist. Featherbeds and blooded horses were favorite spoils of war brought back to England. In th 1300s and 1400s, the King relied on mercenaries hired directly or by contract with his great nobles for foreign wars.

Many lords got men to fight with them by livery and maintenance employment agreements such as this one of 1374: "Bordeaux, February 15. This indenture, made between our lord King John [of Gaunt, of Castile, etc.] of the one part and Symkyn Molyneux, esquire, of the other part, witnesses that the said Symkyn is retained and will remain with our said lord for peace and for war for the term of his life, as follows: that is to say, the said Symkyn shall be bound to serve our said lord as well in time of peace as of war in whatsoever parts it shall please our said lord, well and fitly arrayed. And he shall be boarded as well in time of peace as of war. And he shall take for his fees by the year, as well in time of peace as of war, 133s. ten marks [133s.4d] sterling from the issues of the Duchy of Lancaster by the hands of the receiver there who now is or shall be in time to come, at the terms of Easter and Michaelmas by even portions yearly for the whole of his life. And, moreover, our lord has granted to him by the year in time of war five marks [67s.] sterling by the hands of the treasurer of war for the time being. And his year of war shall begin the day when he shall move from his inn towards our said lord by letters which shall be sent to him thereof, and thenceforward he shall take wages coming and returning by reasonable daily [payments] and he shall have fitting freightage for him, his men, horses, and other harness within reason, and in respect of his war horses taken and lost in the service of our said lord, and also in respect to prisoners and other profits of war taken or gained by him or any of his men, the said our lord will do to him as to other squires of his rank."

Forecastles and stern castles on ships were lower and broader. Underneath them were cabins. The English ship was still single-masted with a single square sail. A navy was formed with over 200 ships selected by the English admirals acting for the King at the ports. Men were seized and pressed into service and criminals were pardoned from crimes to become sailors in the fleet, which was led by the King's ship. They used the superior longbow against the French sailor's crossbow. In 1372, the Tower of London had four mounted fortress cannon and Dover had six.

The war's disruption of shipping caused trade to decline. But the better policing of the narrow seas made piracy almost disappear.

In 1363, Calais, a continental town held by the English, became the staple town for lead, tin, cloth, and wool and was placed under a group of London capitalists: the Merchants of the Staple. All exports of these had to pass through Calais, where customs tax was collected. Merchants who took cloth abroad to various places to sell, personally or by agents, were called merchant adventurers to distinguish them from the Merchant of the Staple.

Waterpower was replacing foot power in driving the mills where cloth was cleaned and fulled [thickened].

A boundary dispute between two barons resulted in the first true survey map. Nine cow pastures were divided by a boundary marked by a shield on a pole which the commission of true and sworn men had set up.

Bethlehem Hospital was used from 1377 to house the mentally ill.

The Law

After the Black Death of 1348 these statutes were enacted: