The Fokker D.XXI was a single-seat fighter aircraft designed and manufactured by the Dutch aviation company Fokker. It served primarily with the Netherlands’ Luchtvaartafdeeling (LVA) (Aviation Department) during the late 1930s, the Finnish Air Force in the Winter War and played a notable role during the opening phase of the Second World War. Although already obsolescent by the standards of 1940, the D.XXI demonstrated surprising effectiveness in combat, particularly in Dutch and Finnish service, where skilled pilots exploited its strengths to compensate for its technical shortcomings. This article focuses chiefly on the Dutch and Finnish variants and their operational history, while also addressing foreign use, like Danish variants.

The NF-5A aircraft were acquired by the Netherlands in the late 1960s to replace the ageing F-84F Thunderstreaks that were still serving in the strike and close-support role within the Royal Netherlands Air Force (KLu). The Netherlands initially considered multiple fighter-bomber options, including the Mirage III, but ultimately selected the F-104G for interceptor duties. A second procurement program was then launched to find a more affordable tactical fighter to support ground forces, leading to the choice of a uniquely Dutch variant of the F-5 Freedom Fighter.

The Belgian Armed Forces—known as Defensie (NL), La Défense (FR), and Belgische Streitkräfte (DE)—serve as the national military of the Kingdom of Belgium. The monarch, the King or Queen of the Belgians, acts as the commander-in-chief. Belgium operates a professional military force, as conscription was officially suspended on February 5, 1995.

The Supermarine Spitfire was first flown by Belgian pilots at the beginning of World War II. The pilots and pilot candidates came from various parts of the world: Europe, North and South America, Africa, and even China. A number of them were from Belgium, having spent time in French, Portuguese, or Spanish prisoner-of-war camps. Most of them joined the Royal Air Force and were assigned to various Bomber and Fighter Squadrons. On February 11, 1941, a Belgian flight was formed within the 609 Squadron. After just a year, their numbers had grown so large that it was decided to establish a full Squadron on February 11, 1942: the 350 Squadron, with the code MN. In November of the same year, a second Squadron was formed: the 349 Squadron, with the code GE. They were equipped with Spitfire Mk II A aircraft from the Royal Air Force.

The Mirage 5BA aircraft were procured by Belgium in the late 1960s to replace the outdated (R)F-84Fs, which were serving primarily as fighter-bombers in the Belgian Air Force. The Mirage was selected from a range of options, including the F-5A, A-4E, and Draken. Belgium became the largest user of the Mirage 5 in history, with over 100 of the type in its inventory.