Which is one of the three most common loads for preconnected attack lines?

The Minuteman load is a highly effective and commonly utilized configuration for preconnected attack lines. This load allows for quick deployment and easy access to the hose, which is critical in emergency situations where time is of the essence. The design of the Minuteman load facilitates a rapid advancement by keeping the hose compact and manageable, making it particularly useful for firefighters who need to quickly engage in operations.

The other types of loads mentioned, such as the flat load, horseshoe load, and saddle load, while also valuable in specific scenarios, do not match the Minuteman load in terms of widespread use and efficiency for preconnected lines. The flat load can be efficient for certain purposes, but it does not allow for the same rapid deployment as the Minuteman. The horseshoe load and saddle load have their benefits in other contexts, but they lack the practicality and quick access that the Minuteman design provides during a high-pressure incident. Thus, choosing the Minuteman load as one of the most common types reflects its practical applications in the field of firefighting.