In the single-player campaign of Call of Duty: United Offensive, Spitfires are seen in the level, "Bomber", acting as escort fighters for number ninety squadron of the RAF, a squadron flying the new American B-17 heavy bomber. These Spitfires help to fight off marauding Bf 109s, but cannot accompany the squadron past the English Channel due to their limited range.
In Call of Duty 2, the Spitfire is never seen up close but can be spotted dogfighting with German Ju 87s during the British North African campaign levels such as "The End of the Beginning" and "Assault on Matmata". The player can get a better view of the Spitfires at the conclusion of "The End of the Beginning": when rejoining Captain Price at the captured German Flak 88, Spitfires can be seen flying by in pairs, returning to base after having established air superiority.
In Call of Duty 2: Big Red One, Spitfire Vc's appear in the level "Baptism By Fire", combating Stukas and Bf 109s during Operation Torch, the British-American invasion of French North Africa. These Spitfires are noteworthy for sporting USAAF insignia rather than RAF insignia. This is accurate, as many U.S. Spitfires fought in North Africa, particularly during Operation Torch. The USAAF was the largest foreign user of Spitfires, with two fighter groups equipped through reverse Lend Lease operating in North Africa and the Mediterranean.
The Supermarine Spitfire was intended to appear in the cut British campaign, in particular, the second mission. It would've likely fulfilled a similar "eye candy" dogfighting role as Call of Duty 2, as the Junkers Ju 87 is also precached within the same set of strings. It would've also dropped bombs in certain set pieces.