Nocturnal Missions are not the best, well compared to the mainstoryline episodes. These 3 episodes are before the first ep, so therefore are prequels.
Gameplay
They don't bring new guns or something, only new maps with reskinned bosses mostly.
Story
Hitler's men are trying to create a new chemical project and so the main scientist behind all of this is Otto Giftmacher, your journey is to kill him and that's E4, dark secret.
In E5 our protagonist is searching for the plans for the chemical project, while searching BJ finds Gretel Grosse the sister of Hans, which is a reskin and the guardian of the plans and that's E5 known as trail of the madman.
At last, E6 is the last in the nocturnal trilogy and you need to find general fatface, who is the project holder behind this project and that's all about E6, confrontation.
Conclusion
If you want to play wolf 3D in the chronological order you can start with the nocturnal missions, but personally I found this trilogy to be weaker than 1-3 but a little reminder in E6M8. Don't rush, collect ammo and health and get a chain gun earlier don't be like me if you play on a harder difficulty.
Gameplay
They don't bring new guns or something, only new maps with reskinned bosses mostly.
Story
Hitler's men are trying to create a new chemical project and so the main scientist behind all of this is Otto Giftmacher, your journey is to kill him and that's E4, dark secret.
In E5 our protagonist is searching for the plans for the chemical project, while searching BJ finds Gretel Grosse the sister of Hans, which is a reskin and the guardian of the plans and that's E5 known as trail of the madman.
At last, E6 is the last in the nocturnal trilogy and you need to find general fatface, who is the project holder behind this project and that's all about E6, confrontation.
Conclusion
If you want to play wolf 3D in the chronological order you can start with the nocturnal missions, but personally I found this trilogy to be weaker than 1-3 but a little reminder in E6M8. Don't rush, collect ammo and health and get a chain gun earlier don't be like me if you play on a harder difficulty.