Billy Don't Be a Hero to ride out and seek reinforcements. (This suggests mounted infantry and a lack of modern two-way radio communications.) In the end, the heartbroken woman throws away the official letter notifying her of Billy's "heroic" death. Paper Lace's version of "Billy Don't Be a Hero" reached No. 1 in the UK Singles Chart on 16 March 1974, and did likewise in Australia, where it spent eight weeks at the top spot. Thereafter, Bo Donaldson's and the Heywoods's version reached No. 1 in the U.S. on the "Billboard" Hot 100 on 15 June 1974, but was dubbed into French for Canada. The
A Town Called Mercy looking to give each episode of the series a distinct feel, showrunner Steven Moffat pitched the Wild West theme to writer Toby Whithouse, suggesting that the episode could be about a town terrorised by a robot. Moffat was keen on putting Matt Smith in a Western setting, who he called one of the last people one would expect to replace Clint Eastwood. Whithouse had previously written the "Doctor Who" episodes "School Reunion" (2006), "The Vampires of Venice" (2010), and "The God Complex" (2011). Moffat had been planning for the first five episodes of the series to have "movie marquee" themes.