What's the hardest test to pass in the U.S. military?

Okay, this might seem like an odd question, but I'm really interested in pushing my limits. I've been thinking about the military and I have this question. What is considered the most difficult test to pass in the U.S. military? It can be physical, academic, or something else. Thank you for any help!

The consensus often points towards the U.S. Navy SEALs' Basic Underwater Demolition/SEAL (BUD/S) training as one of the most difficult to pass in the U.S. military. This six-month training program is known for its extreme physical and mental challenges.

The training is divided into three phases: physical conditioning, combat diving, and land warfare. Designed to push candidates to their physical and mental limits, BUD/S has an attrition rate of about 75 to 80 percent, meaning only about 20 to 25 percent of candidates successfully complete the training.

Physical conditioning includes rigorous workouts, four-mile timed runs in boots, two-mile ocean long-distance swims, obstacle courses, and "Hell Week"—a five-and-a-half day stretch where candidates sleep only about four hours total.

The second phase, combat diving, introduces and develops the underwater skills required of Navy SEALs, including long-distance underwater navigation. This phase is as mentally challenging as it is physically, due to the "drown-proofing" test, where candidates must complete exercises underwater while their feet and hands are bound together.

Finally, the third phase, land warfare, trains the candidates in basic weapons, demolition, patrolling, reconnaissance, and tactics skills.

Just as a note, while BUD/S is often cited as the most challenging due to its notorious Hell Week and high dropout rate, all special operations forces in the U.S. military - such as Army Special Forces (Green Berets), Marine Corps' MARSOC, and Air Force's Special Tactics - have their own rigorous, challenging selection and training processes. Each is unique with its own set of challenges.