I was half expecting to spend the day in the back seat of a humvee, being chauffeured around the base for various photo ops, but to my delight the Major in the charge of the course had other plans. We hoofed miles and miles and miles through the thick Quantico forest, crossed streams, and logged many hours on the base's blacktop roads on one of the hottest days of the summer to give us just a small taste of what the Marines on the other end of my camera were going through.

To protect the integrity and efficacy of the training for future officer classes, the Marine Corps asked that some events not be photographed and that some details be omitted when describing the Combat Endurance Test. Most of the photos in this blog post have been shuffled out of chronological order at the Marine Corps request. For the same reason I won't say how long the test lasted for or how far we (much less the Marines) went, but I will say this was both mentally and physically the toughest assignment I've ever shot. I have a newfound respect for our Marine Infantry Officers and the men who train them.

Marine 2nd Lieutenants muster before loading for the Combat Endurance Test at a pre-4am morning briefing. The CET is the first test of the Infantry Officer Course at Marine Corps Base Quantico in Quantico, Va. Luke Sharrett for The New York Times.

Marines receive a briefing for the Combat Endurance Test in the pre-dawn hours of July 6, 2012.

Infantry officer candidates load into deuce-and-a-half cargo trucks at 4am to start the Combat Endurance Test at Quantico. 

Marines shed their kevlar plates and helmets after being dropped off in an undisclosed location in the Quantico wilderness just after 4am at the start of the Combat Endurance Test.

2nd Lieutenants march during the land navigation portion of the Combat Endurance Test. Participants are not allowed to speak to each other for the entirety of the event. 

A map of Marine Corps Base Quantico in Quantico, Va., home of the Infantry Officer Course.

A sweaty Marine 2nd Lieutenant consults his map during the land navigation portion of the Combat Endurance Test, the first event in the Infantry Officer Course at Marine Corps Base Quantico.

Infantry Officer Candidates endure both physical and mental challenges during the test. 

A Marine 2nd Lieutenant does pull-ups during a fitness portion of the CET.

A candidate does push-ups during the test.

A Marine 2nd Lieutenant works to assemble a Kalashnikov variant during a weapons assembly test.

A Marine 2nd Lieutenant makes his way through the obstacle course during the Combat Endurance Test.

The last event on the obstacle course is a rope climb with full ruck.

A Marine takes a quick moment to catch his breath on the obstacle course.

A Marine 2nd Lieutenant treads water in full gear during a swimming portion of the Combat Endurance Test.

Physical challenges are interspersed with mental ones by design during the span of the course.

A 2nd Lieutenant hustles past a Naval Corpsman reclining in an ambulance during the test.

A Marine jogs to his next station during the test.

Marines nursed injuries after crossing the finish line of the CET.

The rigors of the Combat Endurance Test take their toll on the Marines' feet.

A Marine 2nd Lieutenant naps after completing the Combat Endurance Test, the first event in the Infantry Officer Course at Marine Corps Base Quantico in Quantico, Va. Luke Sharrett for The New York Times.

Thanks for looking!

**Photos copyright Luke Sharrett and The New York Times**