What is the most difficult US military school?

Some of the foreign schools rival the obvious choices in US. British Commando, Spetsnaz, FFL etc. I knew a few USMC Infantry types that went through Ranger Course, and none said it was easy. I've read about SF and it sounds tough. Seems there was one for SFOD-D that entailed a very lengthy hump with heavy pack in mountains of W Va. Training for many of those Tier 1 assets is classified.

18D Special Forced Medical Training in the SFQC Pipeline. I saw the best and brightest fail- SEALs, Rangers, Force Recon, PJs, Airborne, etc.
mentally and physically challenging, years long course, language qualification as well.

I'm going to take a different approach to this. The Medic can be more demanding than some other schools. Think about it. They have to be willing to run to someone hurt bad, maintain their cool, treat life-threating injuries while being shot at. I'm sorry but when you get to the end of school and you realize what is going to happen......

Ultimately... it depends on the individual. Some folks would say SERE... then there's the myriad of courses for the SpecOps Warriors... then there are the schools that require skull sweat.

For some, boot camp is an insurmountable challenge.

It's an individual challenge, only the induvidual can say what was toughest FOR THEM.

Military Police school

Hard Knocks. They're the hardest ones to get over.

The key word here is challenging. Physically challenging, mentally challenging or a combination of both? And what's the standard for "challenging?" Some one who completes a physically challenging course may not be able to complete a mentally challenging course and vice versa. With no basis for comparison(other than a couple of visits to San Diego) to other service schools, I'd have to pick Ranger course as the most physically challenging. From observation, I'd choose the entire curriculum for qualification as an SF medic probably as the toughest combination of physical and mental challenge. Mentally, the most challenging course I attended was the Prefix 5 course. We even had a couple of Rangers and a Recon Marine fail that one.

Usmc martial arts instructor course.

From my time at Harmony Church and Camp Rudder I would have to say Army Ranger School. However, I have never been to SFAS or Seal School so I can.t make a comparison.

Air Force PJs, without a doubt; the washout rate is in the 90% range....