Kate Middleton worshipped at St Clement Dane's Church, a church specifically for the RAF, in central London.
The royal is the Honorary Air Commandant - effectively a patron - of the organisation.
She took over from the Duke of Edinburgh Prince Phillip, who held the position for 63 years, in December 2015.
RAF Air Cadets currently provides skills and training to more than 40,000 young people aged 12-19.
Several events will be taking place throughout 2016 to mark 75 years since its beginning, when it was launched to give younger civilians air training before they went to fight in World War II.