In a flashback sequence, we get to see the other 5 serum subjects revolting against their Russian controllers.
If I remember correctly, the scene basically ends with one of the Russian overlords forcing Bucky to act as his shield to get him out of there.
My question now, how does this unruly bunch actually get subdued and frozen? Did they do this themselves?
The long and the short of it is that it's never explained, in either the movie or the source comic. They were most likely gassed or controlled in some other way, but they somehow ended up back in cryogenic stasis.
The Russians you speak of (presumed to be doctors too) tried to test out whether or not their experiment was a success or not. It was a glad moment that it did for them, but only to cause a riot.
Now, to control 5 people, who were HYDRA's top killers EVEN BEFORE the super-serum was given to them, we don't have to think twice that HYDRA didn't have any back-up plans.
Although Bucky was asked to escort the commander for that moment, which he managed to do, I would like to point to the fact that this shows how HYDRA controls Bucky.
Those few words are enough for Bucky to do whatever is asked once he is compliant. And they programmed him as such that not only a handful individuals, but ANYONE who can recite the words (like Zemo) can control HYDRA's super-soldiers.
To conclude, I will say that for the particular moment shown in the movie, the commander asked Bucky as he was the only backup he had in that prison. Once he was out of the prison, the Winter Soldiers were frozen after being controlled (by physical or mental means or both).
Please refer to official Marvel backstory here.
