Just about everyone paints Bruce as a pain in the arse, not a lethal monster.
Notoriously finicky, Bruce was really a collection of three $US150,000 mechanical sharks that were each capable of only a modest range of movement (one went left-to-right, one went right-to-left and one exclusively did underwater scenes). Why could two of the sharks only swim one way? Because the non-camera-friendly side was nothing but exposed gears. From Time:
Bruce was fairly programmed for mishap. In order to use him, a twelve-ton steel platform, to which the mechanical shark was attached by a 100-ft.-long umbilical cable, had to be sunk to the ocean floor. The controls on the platform were operated by 13 technicians wearing scuba equipment.
Bruce sank when he made his debut. During his second test on water his hydraulic system exploded. "That shark," says Producer Brown, "was like owning a yacht. We had to dredge a place for it to rest, we had to park it, guard it, stroke it, hide it from the public."
Bruce caused delays for the open water shoot which skyrocketed Jaws' budget to $US7 million (about $US27 million today). Of course, Jaws would eventually be widely recognised as the world's first summer blockbuster as it's since made $US470 million (or $US1.9 billion today).