In an extended programme for Remembrance Sunday, Countryfile explores Word War One's lasting legacy on the landscape of the western front and the part played by those on the home front in winning the war. Matt Baker uncovers a subterranean network carved out by allied troops from the chalk of Arras and learns about the role played by mule-men like his great-grandfather in the war. Ellie Harrison reveals the iron harvest of bombs still unearthed by farmers today, Tom Heap goes on a very personal investigation to the start of trench warfare, John Craven reveals how we adapted tractors to make the world's first tanks and Adam Henson discovers how man's best friend became his greatest ally when dogs were trained for front-line duties by the British army.