Which component does the APU directly support while the C-130J is on the ground?

The Auxiliary Power Unit (APU) on the C-130J directly supports the air conditioning system while the aircraft is on the ground. The APU provides the necessary bleed air and electrical power that the air conditioning system requires to operate independently of the engines. This is particularly important during ground operations, as it helps maintain a comfortable environment in the cockpit and cabin for both the crew and any personnel on board.

While electrical systems and navigational systems may also receive some support from the APU, they are not its primary role in ground operations. The weapons system is typically not supported by the APU when the aircraft is stationary, as the APU's function does not include armament systems. The core function of the APU is to ensure that critical systems, like air conditioning, are fully operational, ensuring the crew can effectively prepare for missions in a comfortable environment.