Which type of fire requires major changes in direction without significant elevation changes?

The type of fire that requires major changes in direction without significant elevation changes is swinging traverse. This technique is employed to engage targets that are moving laterally across the field of fire. The key characteristic of swinging traverse is its horizontal movement where the gun remains at the same elevation, allowing for quick adjustments to cover various angles of attack without needing to alter the height at which the weapon is fired.

Sustained fire typically refers to maintaining a continuous rate of fire to achieve a specific effect on the target over a period. Fixed fire focuses on shooting at a single predetermined target location without changing direction. Sweeping fire, while involving lateral movement, often includes a combination of elevation adjustments as well, distinguishing it from the purely horizontal adjustments made in swinging traverse. Thus, swinging traverse is the most accurate answer as it explicitly addresses the requirement for significant changes in direction with no elevation changes.