Which helicopter is not designed for amphibious assault or troop transport?

The AH-1W Cobra is primarily designed as an attack helicopter, focused on providing close air support, anti-armor engagement, and armed reconnaissance. While it may accompany troop transport operations and contribute to offensive maneuvers, it is not specifically intended for amphibious assaults or troop transport. Its role emphasizes firepower and support, positioning it distinctly from the other helicopters listed, which are designed to transport Marines and equipment in assault scenarios.

The CH-53D Sea Stallion and CH-46E Sea Knight are both helicopters specifically built for troop transport and amphibious operations. The MV-22B Osprey, with its tilt-rotor design, provides versatile transport capabilities in combat and is also tailored for amphibious assault roles. In contrast, the Cobra's design focuses on engagement rather than troop movement, thus confirming its classification apart from those other models.