1) Cannon 2) Upper cannon 3) Western plate armour 
A rerebrace (sometimes known as an upper cannon) is a piece of armour designed to protect the upper arms (above the elbow). Splint rerebraces were a feature of Byzantine armour in the Early Medieval period. The rerebrace seems to have re-emerged in England, in the early 14th century. As part of the full plate armour of the Late Middle Ages and Ren...
armour for the upper arm
• (n.) Armor for the upper part of the arm.
Rere'brace` noun [ French arrière-bras .] (Anc. Armor) Armor for the upper part of the arm. Fairholt. 
[n] - cannon that provides plate armor for the upper arm
upper cannon noun cannon that provides plate armor for the upper arm