What are the barrel coverings seen on tanks in pictures/videos for?

by Vyncis

For those who don't quite get what I mean, the covering on the end of the barrel when a tank was not in combat.

At a guess, it is to stop dust and whatnot from getting in. Is that correct?

Was another intended/accidental purpose to stop saboteurs from stuffing in obstructions when no one was around?

crispychoc

Often when travelling a tank kicks up a lot of dirt, a bit of dust would matter, small rocks could stop the projectile from clearing the barrel, thus obstructing it. The explosive force would go back into the tank, which is not great for the tank operators.

A tank gunner checks for obstructions in the barrel before loading, but during transportation or when not in use it's easier to put the hood on it.

Also stops rain from coming in.