There were around TWENTY (20) mainline titles in the Call of Duty series, not counting expansions, mobile versions, or remastered editions.
There are currently SIX (6) Call of Duty World War II games
Call of Duty, released in 2003, immerses players in World War II battles. Developed by Infinity Ward, it's a landmark FPS available on various platforms.
Call of Duty 2, a sequel by Infinity Ward, plunges players into WWII through Red Army, British, and US perspectives. Released 2005, available on multiple platforms.
Call of Duty 3, a FPS released on Nov 7, 2006, by Treyarch. Not by Infinity Ward, it's a WW2 shooter on consoles.
Call of Duty: World at War, developed by Treyarch, immerses players in WWII combat, introducing Black Ops storyline and iconic Zombies mode.
Call of Duty: WWII, 14th installment by Sledgehammer Games. Set in WWII's European theatre, follows 1st Infantry Division's battles, centered on Operation Overlord.
Call of Duty: Vanguard, the 18th installment, features WWII's special forces origins, with intense battles across platforms, including Zombies mode collaboration with Treyarch.