Between November 1973 and April 1974, the sharks were fabricated at Rolly Harper’s Motion Picture & Equipment Rental in Sun Valley, California
Three full-size pneumatically powered prop sharks—which the film crew nicknamed ”Bruce” after Spielberg’s lawyer, Bruce Raimer—were made for the production…
…a ”sea-sled shark”, a full-body prop with its belly missing that was towed with a 300-foot (roughly 100-m) line, and two ”platform sharks”, one that moved from camera-left to -right (with its hidden left side exposing an array of pneumatic hoses), and an opposite model with its right flank uncovered.
Their construction involved a team of as many as 40 effects technicians, supervised by renowned mechanical effects supervisor Bob Mattey, best known for creating the giant squid in 20,000 Leagues Under the Sea.
After the sharks were completed, they were trucked to the shooting location. In early July, the platform used to tow the two side-view sharks capsized as it was being lowered to the ocean floor, forcing a team of divers to retrieve it.
The model required 14 operators to control all of the moving parts.
The prop sharks frequently malfunctioned owing to a series of issues including bad weather, pneumatic hoses taking on salt water, frames fracturing due to water resistance, corroding skin, and electrolysis.
From the first water test onward, the ”non-absorbent” neoprene foam that made up the sharks’ skin soaked up liquid, causing the sharks to balloon, and the sea-sled model frequently got entangled among forests of seaweed.
Spielberg later calculated that during the 12-hour daily work schedule, on average only four hours were actually spent filming.
The delays proved serendipitous in some regards. The script was refined during production, and the unreliable mechanical sharks forced Spielberg to shoot many scenes so that the shark was only hinted at.
SPIELBERG: ”The film went from a Japanese Saturday matinee horror flick to more of a Hitchcock, the less-you-see-the-more-you-get thriller.”
SPIELBERG: ”The shark not working was a godsend. It made me become more like Alfred Hitchcock than like Ray Harryhausen.”
The acting became crucial for making audiences believe in such a big shark. SPIELBERG: ”The more fake the shark looked in the water, the more my anxiety told me to heighten the naturalism of the performances.”