On a HEMTT, which hose connects to the service coupling?

The blue hose is the correct answer because it is designated as the service hose for the HEMTT (Heavy Expanded Mobility Tactical Truck). This hose is specifically used for connecting to the service coupling of the vehicle, allowing for the transfer of fuel or other necessary fluids during operations.

Each color-coded hose has a unique function to ensure that the right fluids go into the right systems, preventing contamination and operational errors. The red hose typically pertains to a different service or system, while the green, yellow, or any other color hoses would be associated with other functions or different types of fluids. Understanding this color-coding system is crucial for safe and effective operations while maintaining the equipment.