The process of manufacture was patented in 1935 by Rowntree’s. Registration of the trademark and manufacture to market started soon after.
In 1935, Rowntree’s launched Aero into the UK, followed by the mint variation in the 1970s. Wrapping was brown (green in the mint version) and displayed the “Rowntree’s” script logo and the large word “AERO”, along with the slogan “Hold on tight or I’ll fly away!” below the “AERO” name. The words “Aerated Milk Chocolate” (“Aerated Milk-Mint Chocolate” for the mint version) were seen multiple times in the word “AERO.” In the 1970s, an advertisement was aired in which kids flying a kite thought the kite was an Aero bar. Then, brown and white bubbles would fly out of the imaginary bar to form the Aero wrapper. In 1988, Rowntree Mackintosh (as it then was, having merged with Mackintosh’s in the 1960s) was losing money and was sold to Swiss company Nestlé, who was already famous for its own Nesquik flavoured milkshakes and Milkybar white chocolate bars. Nestle continue to manufacture many former Rowntree bars and products, and until 1993 several chocolate products continued to use the Rowntree/Rowntree Mackintosh brand name. Since then only the sugar confectionery bears the old Rowntree name (Fruit Pastilles, Fruit Gums, and so on).
Info gleaned from Wikipedia