The Gillies anaesthetic machine was produced commercially after 1941. It was probably the first British true circle apparatus. Notably it incorporated a vaporiser inside the circle. There were serial modifications culminating in the Mark III apparatus of 1951, which continued in use through the 1960s. From 1955 the superior efficiency in carbon dioxide absorption of a true circle apparatus over the rival Coxeter-Mushin 'circle' absorber became realised.