Eisenstein pioneered an early groundbreaking technique. What is it called?

"The Battleship Potemkin by Russian filmmaker, Sergei Eisenstein."

What special effects used in the making of this early film?

In The Battleship Potemkin, Sergei Eisenstein pioneered an early groundbreaking technique called the tracking shot. In the infamous 6-minute long scene of the Odessa steps, he depicts the tsarist troops firing upon the crowd, including mothers and children.

The scene, shot from the side of the stairs at first, is made to establish a sharp contrast between the cold military organization on one hand and the civilian chaos on the other hand.

The climax is reached through a particularly innovative shot of a cradle hurling down the stairs after the death of the mother, which combines the technique of the tracking shot (camera on rails to follow an object) with that of the high-angle shot since the cradle is seen from above as it falls down the stairs.