The Cadet Force is the largest single organisation in the School, numbering 460 cadets. Eighteen members of staff provide a varied and exciting training programme every Wednesday afternoon during the term, with two field weekends, one in September and one in April.

The CCF comprises three sections: the Army, the Royal Navy and the RAF, and is compulsory for all pupils in the Fourth Form. All three sections have a common core of Drill, Turnout and Skill at Arms. The RN Section then specialises in rowing, sailing and power boating, the Army Section in infantry skills and tactics, and the RAF Section in flight training. At the end of their Fourth Form year cadets may leave or decide to stay in the CCF and enter one of the specialist training sections: Advanced Infantry, NCO training within the Services, Fire and Rescue, Adventure Training and Diving.

Every cadet will undertake at least one camp during School holidays, some of which are aimed towards gaining qualifications, whilst others are aimed at developing leadership and teamwork skills.

In addition to single service Army camps and courses, all Army cadets are able to attend other tri-Service cadet camps and courses during any or all of their time within the CCF. These include the annual sub-aqua diving camp in the Red Sea, the annual Alpine Skiing Development Camp in Switzerland, the annual Adventurous Training camp in Wales or Scotland, annual target rifle shooting at Bisley, as well as external camps and courses run by the three regular Armed Services, ranging from parachuting to sailing.

The Oundle School Corps dates back to 1902, as the 'Rifle Corps' 1st (Volunteer) Battalion the Northamptonshire Regiment. Since 1958, the Cadet Corps at Oundle has continuously maintained all three Service sections. Success and recognition for cadets has been achieved at national levels; Oundle has produced three finalists drawn from the country’s best 200 cadets in The Duke of Westminster Award.