Knight in Armour is Episode 6 of Season 1. It aired on January 26th, 2003. Here's the synopsis from TV.com:
Actor and fight master Peter Woodward returns to the days of chivalry to find out why personal armor developed--from horn and linen to chain mail to full plate. We visit an armorer's workshop to see how it was made, and our expert team tries on various types, including the classic medieval plate armor, to assess their strengths and weaknesses, and tests fighting techniques with various knightly armor-piercing weapons. Then, we put the armored knight in his proper place--mounted on a charger!
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