The Royal Gunpowder Mills are a former industrial site in Waltham Abbey, England.It was one of three Royal Gunpowder Mills in the United Kingdom (the others being at Ballincollig and Faversham). Waltham Abbey is the only site to have survived virtually intact. The Royal Gunpowder Mills, Waltham Abbey, were in operation for over 300 years. Starting in the mid-1850s the site became involved in the development of revolutionary nitro-based explosives and propellants known as "smokeless powder". The site grew in size, and black powder became less important.