But mostly you marvel at how they go about their days: run with M-16s flapping against their backs for miles at high noon when it's topping 115 degrees just for the exercise; how they wear long sleeves, pants, suede desert boots, 30 pounds of armor and man a gun on top of a Humvee, faces encrusted with dust; how they work at least 12 hours a day, every day, with no days off, under a constant threat of mortars and rockets.
You wonder where they find the energy to play basketball at midnight (the military police do, reliably, every night, sometimes listening to rap, sometimes heavy metal and once Michael Jackson's greatest hits.) How they detach themselves sufficiently from the danger to teach fellow Marines to salsa after dinner. How in the dark of night they practice martial arts to a hypnotic drum beat, lit only by pale green chemlights broken at their feet.
It probably has something to do with the fact most of them seem to be around 20 years old, and many are in a combat zone for the first time -- something they actually relish.
"Marines run toward gun fire, not away from it," a senior commander told me.
And the worse conditions are, the better Marines seem to like it. Marines at a dusty outpost on the Syrian border take great pride they are not serving instead at "Camp Chocolate Cake," as they refer to al-Asad, home of the 7th Regimental Combat Team. Everything here is relative. To an American eye it is downright bleak. But inside row upon row of plywood buildings it is cool. A Marine doesn't care how hot he gets as long as he knows he has a cool place to sleep, I'm told.
An air conditioned place to sleep is one of the things 1st Marine Division Commander Maj. Gen. Jim Mattis requires for his troops.
It's a change from some previous practices in the military. In Afghanistan in the blistering hot summer of 2002, Army soldiers were chided for complaining to me about their rudimentary tents. Once the sun came over the mountains, they heated up quickly and it was impossible to sleep -- a bad situation for soldiers mostly carrying out night missions.
Mattis has also introduced the notion of making the regimental command headquarters a psychological safe haven for battle-weary Marines. If they get jittery at the front, they can fall back on the RCT headquarters where they can get cleaned up, a shower, sleep, counseling from other Marines, and medical attention.
"The regiment is safe in his mind. It allows him to catch his breath. When he's ready to go (he returns to his unit) and he regains his manhood, right there with his buddies," Mattis explained, over breakfast at Camp Chocolate Cake, where he has come by helicopter to welcome a new set of Marines to the front.
"We never want to evacuate a combat stress (Marine) behind the regiment," Mattis said.
The approach is paying dividends, according to Mattis' statistics.
"We've only had one guy leave in a division of 20,000 (in the last six months) and that was a pre-existing psychiatric disorder," he said proudly.
Last year only three left of the 25,000 in the 1st Marine Division in Iraq, a testament to what Mattis calls a humanistic approach to keeping military personnel healthy in both mind and body.
The 1st Marine Division has had a remarkable record by anther grim measure: suicide. Only two Marines have committed suicide in the entire expeditionary force.
"We just do not understand what happened. He was doing good," Mattis said of one case. He has clearly reviewed the details.
Some of his success in maintaining morale so far may be attributable to Mattis' policy of assigning every Marine a "combat buddy" -- someone they trained with at home and with whom they are deployed, so a Marine is never alone in a unit as the new guy.
"People fight better then they know each other," he said. "The more stability we give them, the more anchors they have the better. (At this age) they don't have the emotional shock absorbers that you and I do."
He derides the experience in Vietnam when the newest guy -- FNG, in profane military parlance -- was sent out his first night to stand point to see if he'd get shot.
"You don't do that with human beings. You bring them in and let them be part of a team," he said.
A recent report on military mental health showed an alarming number of combat veterans from Iraq are suffering from post-traumatic stress disorder, something Mattis believes can be mitigated, albeit not wiped out, by hands-on commanders who watch for signs of stress and help troops deal with it.
"I don't have any use for the strong, silent type," he said.
Mattis commands a powerful loyalty and respect from his troops.
"He leads from the front," one Marine noted in the cool and noisy morale, welfare and recreation tent at Camp Blue Diamond. It has a pool table, a ping pong table, foosball, Nintendo, a large-screen TV, 20 Internet monitors, a library filled with cast off magazines and paperbacks, and a seemingly perpetual dominos game that somehow the Marines have turned into a full contact sport.
When Mattis' "jump platoon" goes out in a convoy -- it is regularly attacked and has been hit by improvised explosive devices at least twice -- it is not uncommon for the general to have his head out the turret, assuming the same risk as the gunners, say Marines.
A lieutenant colonel gave a more specific example of leading from the front: When the Iraqi-led Fallujah Brigade was created, Mattis decided it needed a test run to see if the native force could actually keep order in the city after weeks of fighting. He sent a Marine convoy through town to see if it would be shot at. He was in the convoy.
For all his tenderness to his Marines -- whom he usually addresses as "gents" -- he clearly enjoys a battle.
"The first time you blow someone away is not an insignificant event," he tells about 200 Marines, sitting on the ground under a metal windbreak against a cliff in Al Asad.
"That said, there are some a--holes in the world that just need to be shot. But you go on and find your next victim or he's gonna kill you or your buddy. It's kill or be killed," he said.
"There are hunters and there are victims. By your discipline, cunning, obedience and alertness, you will decide if you are a hunter or a victim. ... It's really a hell of a lot of fun. You're gonna have a blast out here!" he said, with marked glee. "I feel sorry for every son of a bitch that doesn't get to serve with you."
He is also icily clear with what he expects of the new Marines in the theater, who are much needed reinforcements and relief for departing troops.
"You must know the commander's intent: (Our motto) is 'no better friend, no worse enemy.' But I have added: 'First do no harm.' No harm to the innocent. No harm to a prisoner, ever. This is the Marine Corps," he barked.
Referring to the reserve soldiers who abused and humiliated prisoners at Abu Ghraib, Mattis said: "They were undisciplined, sorry-ass excuses for soldiers. We will not cost America one ounce of its moral authority," he said.
"How you treat people is very, very important. We're not gonna become racists. They (the enemy force) want you to hate every Iraqi out here. ... You treat those women and children the way you do your own. You make certain you don't do anything that would smear the Marine Corps.
"It is absolutely essential you know what I won't f--ing tolerate," he said, and related the details of a recent case in which a Marine administered an electric shock to a detainee he had in jail. He was swiftly court-martialed.
"He thought it was funny. It is, if you like five years in Leavenworth (prison)," Mattis said.
"You are free men. No one forced you into the Marine Corps. You are going to prove the enemy wrong out here," he said.
Mattis is as likely to mention a battle in ancient Rome as he is in Vietnam when making a point to his troops. Every conversation with his Marines seems an opportunity for some history and criticism, usually so subtly the Marine doesn't realize he has been corrected. He feels like he is changing his path on his own.
Mattis is thoughtful without being calculating, and includes his team -- which includes me by sheer proximity from time to time -- in on his leadership decisions.
While in Asad after a brief stop on the Syrian border, he learned of a coordinated and deadly mortar attack on his headquarters base at Blue Diamond. It seriously injured five. At least one -- a well-loved sergeant -- died from his wounds.
Mattis sat on the information for the duration of a solemn helicopter ride. When we landed, he gathered us together and broke the news.
"Now we're going to go in there like nothing is wrong. Cool and calm. Cool and calm," he said, imbuing everyone in the circle with responsibility for maintaining morale.
There are plenty of Marines who have concerns about the original case for the war. They are certainly a minority, and one that no doubt singled me out to discuss their views because of my fairly unusual uniform on base (straw hat, long skirts, braids). But none who question the case for war doubt what will happen if they are pulled out before the job is done: This place will devolve into murderous anarchy, and quickly. There is a mental separation here. The debate about the war is one thing. The commitment to fighting it is quite another. They mourn every loss of a comrade, but they accept it as part of the job. There is an obscene bumper sticker Marines are fond of. It says "U.S. Marine Corps: Because a Natural Death is for P--."
Late one night, a female officer was leaving the command operations center when she said pleasantly to a corporal standing guard: "How are you, Marine?"
The corporal was completely alone in the pitch-black loggia of one of Saddam's former palaces, and would be there for hours more before he was relieved.
"Motivated!" he thundered back, cheerily, from the dark.