Everything is in place. The Cinematographer has given the appropriate instructions to the camera operators. The actors/actresses are in place and have fully rehearsed their lines. The Director is quiet but is studying the upcoming scene with acute intensity, and nods to his Assistant Director (AD). The AD asks “Is everybody ready”? And then the AD says, “Roll sound”. After the cameras are turned on and sync up with sound, camera operators shout “speed”. Then the slate is clapped in front of the camera to give the editor an image of where to sync the sound to the picture. All of the aforementioned is the combined efforts of Unit Production Managers (UPM), Assistant Directors, and camera/sound crews to capture what could be just a few seconds of footage. The Director of a film already has the weight of the world on his/her shoulders to give his respective financer (a movie studio) the best possible product for distribution. The Director certainly needs the help of UPMs and ADs, but some Directors go a major step further by utilizing 2nd Unit Directors.
2nd Unit Directors often capture aerial and action sequences in remote locations that the Director sometimes may steer away from to concentrate on key dialogue intensive scenes. 2nd Unit Directors have their own crew who mimic what the main unit is accomplishing on the majority of the movie shoot. Their camera crews are careful to have their shots (including lighting, film-stock, and camera movement) match the main crew’s efforts.
Remember the desert chase sequence in Steven Spielberg’s classic Raiders of The Lost Ark? Or how about Jason Bourne driving an Audi off the rooftop of a New York building while fleeing a hailstorm of bullets in The Bourne Ultimatum? Sure Spielberg is a great director and Paul Greengrass is a good director. But their 2nd Unit Director(s) deserve the credit for the aforementioned action sequences. From what I have gathered from online articles and Blu-ray/DVD commentaries, Spielberg predominantly does not use 2nd Unit Directors. However, Christopher Nolan and Quentin Tarantino are the only major directors (at least to my knowledge) that have never used 2nd Unit Directors. They indeed have UPMs and ADs that assist their vision, but Nolan and Tarantino are involved in every scene. Nolan donned a scuba tank and wetsuit to oversee the under water sequences of Inception. Imagine the dedication that this man has put into the upcoming The Dark Knight Rises. Tarantino fans can rest assured that no gut-wrenching swordplay scene in the Kill Bill series or memorable Nazi annihilation scenes in Inglorious Basterds was the work of a talented unsung hero.
A great book to read on the roles and responsibilities of a film crew can be found in Frederick Levy’s “Hollywood 101”.