The katana was originally thought to be a usable weapon in Call of Duty: World at War. However, it seems to have been replaced by the bayonet as the katana is unusable by the player and only seen being wielded by some Japanese soldiers during certain parts of the campaign mode. In the first mission, "Semper Fi", a Japanese soldier playing dead stabs Rooker with a katana. Another slashes Miller across the shoulder with a katana as he tries to escape with the other Marines . Also, in the last part of "Little Resistance", Sgt. Tom Sullivan gets killed by a Japanese Banzai Charger wielding a katana. Katanas are usually replaced with the Bayonet by the Japanese soldiers, however they can be seen on some of the soldiers' uniforms even if they are not used.
Examination of the game files reveals two images resembling that of menu and pickup icons for the katana, hinting it was originally going to appear as a usable weapon at some stage of development, at least until it got scrapped.
The Katana is seen on some Japanese enemies through campaign and on Takeo Masaki co-op model, but they are all unusable.
Though many enemies are wearing the katana during the Marine Raiders campaign, it is only seen used three total times in the entire game; during the flare ambush in "Semper Fi", right before the escape from Makin Atoll in Semper Fi and to kill Sgt. Sullivan at the end of "Little Resistance".
Tank Dempsey occasionally makes remarks about how great it'd be to use Takeo's Katana, but then points out it must just be for decoration, much to his disappointment.