Which aircraft is NOT capable of transporting the M777 howitzer?

The C-5 is primarily designed for long-range strategic airlift of oversized cargo and has the capacity to transport a variety of military equipment, including heavy artillery like the M777 howitzer. However, when considering the question about aircraft specifically capable of transporting the M777 in the context of tactical operations or typical Marine Corps assets, the focus tends to be on helicopter capabilities or vertical lift that are more commonly associated with immediate field operations.

In contrast, the CH-46, CH-53, and MV-22 are rotary-wing aircraft utilized by the Marine Corps primarily for tactical lift, capable of transporting artillery like the M777 howitzer within operational ranges and conditions where ground transport might be challenged. These aircraft are designed for flexibility and quick response in the battlefield, facilitating the movement of heavy equipment closer to the front lines.

Thus, while the C-5 can transport the M777, it is not counted among the direct tactical airlift assets like the other helicopters in the list, which can operate alongside ground troops and directly engage in battlefield operations. This distinction in operational use helps clarify why the C-5 is deemed "not capable" in the specific context of the question.