Drone 2 is a scrapped enemy from Duke Nukem 3D. Sprites and remnants of code can be found in the December 1994 prototype, LameDuke. A similar enemy, known simply as the Drone, is fully coded and appears on many levels in LameDuke, but there is evidence in the game's code that the two were completely separate enemies.
Drone 2 is a very incomplete enemy; the only coding for it are five directions for one frame of animation, and the only sprites for it are front, side and back views.
Three of those enemies can be seen flying in the distance in the still of the title and loading screen, one of them firing. The green Drone is also featured in the image, confirming that Drone 2 is not an early design for the other drone but another enemy altogether. In addition, the green Drone is sometimes labeled "DRONE1" in the game's code, suggesting a plurality of drone types was planned from the beginning.