What military role does the F-35B Lightning II fulfill?

The F-35B Lightning II is a multi-role stealth fighter designed to perform a wide range of missions across different domains. Its capabilities encompass close air support, which involves providing ground forces with aerial support in combat situations, as well as fighter escort missions, where it ensures the safety of other aircraft, particularly bombers or transporters, by countering potential threats in the air.

Additionally, while the F-35B is not primarily designed for transport operations, its versatility allows it to operate in various roles that may support transport missions under certain circumstances, especially in a combat or multi-domain operation context where air superiority is vital for safe transport.

This multi-faceted use makes the F-35B a valuable asset for modern military operations, particularly for the U.S. Marine Corps, which often requires aircraft that can adapt to various operational requirements on the battlefield. Hence, recognizing that the F-35B fulfills multiple roles, the most comprehensive answer encompassing its capabilities is "All of the above."