After the success of Red (2010), Ernest Borgnine hoped he'd be around to reprise his role as Henry the records keeper in a sequel. When interviewed in April 2012, he mentioned there was talk about it over the years and made one request to the producers; "I told them if they do it, I want to carry a gun this time." He kept in touch with screenwriters Jon Hoeber and Erich Hoeber and would have had a major role in an early scene. When Borgnine passed away in July 2012, three months prior to the start of production, his scenes were re-written and featured an uncredited Titus Welliver.
(at around 29 mins) The father in the childhood photo of Han Cho Bai (Lee Byung-hun) is Lee's real father.
(at around 1h 30 mins) The diplomatic vehicle number plates, while only props, are designed to look authentic. The first three numbers on a U.K. diplomatic plate tell you which country to which it belongs. 182 is assigned to Iran.
Due to strict U.K. gun laws, producers couldn't import the higher caliber guns they desired.
Frank (Bruce Willis) and Marvin (John Malkovich) pursue The Frog (David Thewlis) using expensive wine as bait due to The Frog's affinity for fine wines. Malkovich is a wine connoisseur who markets wine under his own label from his estate in France.