J Is For Jupon...

Jupon

Jupon ~ A type of sleeveless surcoat worn over the armor in the 14th century.

Jack

Jack ~A defensive coat, either of several layers or quilted leather or linen, often reinforced with metal studs or small plates

As for weapons, well, what's a war without ships?

Junk ~ A junk is an ancient Chinese sailing vessel/ship design still in use today. Junks were developed during the Song Dynasty (960-1129) and were used as seagoing vessels as early as the 2nd century CE. They evolved in the later dynasties, and were used throughout Asia for extensive ocean voyages. They were found, and in lesser numbers are still found, throughout South-East Asia and India, but primarily in China, perhaps most famously in Hong Kong. Found more broadly today is a growing number of modern recreational junk-rigged sailboats.

Junk

And due to the limited number of 'J' items, I bring you a 'J' related, medieval sport:

Jousting

Jousting ~ Jousting emerged in the High Middle Ages based on the military use of the lance by heavy cavalry. It transformed into a specialised sport during the Late Middle Ages, and remained popular with the nobility both in England and Germany throughout the whole of the 16th century (while in France, it was discontinued after the death of king Henry II in an accident in 1559).