If the balloon goes up, something happens that causes a situation suddenly to become very serious. On the Saturday the balloon went up. Henry said he would be going out and not returning until the Sunday afternoon. Sara told him to take all his things and not to return at all. On the line was his solicitor warning that the balloon was about to go up. Note: In the First World War, balloons were used both to protect targets from air attacks, and to observe the enemy. The fact that a balloon had gone up therefore indicated that trouble was coming.