Robin Williams opposed the war in Iraq. His many comedic riffs that punctured the rationale for the 2003 invasion, and the president who ordered it, are evidence enough.

Yet his affection for the warriors sent to carry out the nation’s grim and bloody business in Southwest Asia was on display each time he left home and family at Christmas to go overseas and join the U.S.O. holiday tours for the troops.

His successes on TV and on stage, in film and in stand-up clubs, have been amply noted following his death on Monday. But his audiences, especially among the troops, never knew how hard, really hard, Mr. Williams worked at his craft.

I observed his comedic diligence, genius and humanity up close during two of his intense, raucous U.S.O. tours of Iraq and Afghanistan; in 2004 and again in 2010. (In all, he made four holiday barnstorming visits to the wars.)

Most of the comics, musicians, movie stars, athletes, cheerleaders and models who cross the badlands of the combat zones with the U.S.O. understandably hang out before each show in the climate-controlled tents that serve as a sort of barren-desert green room for the talent and the traveling V.I.P.’s.

Not Mr. Williams.

Long before his stand-up set was scheduled, he would quietly wander the audience starting with the very back rows, immediately recognizable, of course, and always agreeable to posing for selfies and signing autographs.

Actually, though, he was on an intelligence-gathering mission.

He would engage in casual conversations, with jokes and impersonations and heartfelt talk full of “Where ya’ from?” and “How ya’ doing?” and “Thanks for what you do here.”

But he was really working the crowd to pick up the flavor and the vibe — and even the commanders’ personalities and quirks — of every desert outpost to produce a personalized routine for each location.

During one stop at a secret airfield in the Persian Gulf region — an air base so highly classified that its location and mission were subject to a blackout agreement imposed on all civilians aboard the U.S.O. tour — Mr. Williams brought gasps and then cheers when, from the stage, he cracked wise about exactly what they did there.

All you do is fly the world’s most expensive model airplane, he said — in this case, the Global Hawk, one of the prized intelligence drones just entering top-secret service at the time.

The long voyages — U.S.O. tours can cover more than 20,000 miles by airliner, cargo plane, helicopter and armored troop transport — gave Mr. Williams time to engage in another hidden passion, reading. His kit bag was filled with books of fiction and nonfiction, often history. All were source material for his routines that skewered the world as we know it or as he saw it.

And he also devoured books on current affairs, about which he had a keen and sly eye.

Reporters who travel on the U.S.O. holiday tours are not on assignment to write theater reviews, of course. They use the trips — hosted by the chairman of the Joint Chiefs of Staff — as an express bus into and around the war zones. This is tradecraft: Arriving at a base with the nation’s highest-ranking military officer produces a local command staff amiable for interviews.

On one flight out of Afghanistan aboard a cavernous C-17 transport plane, Mr. Williams saw two correspondents sitting in the hard-backed jump seats for paratroopers that line both walls, pounding articles into their laptops after analyzing unclassified military briefing slides of the war effort that had been provided by the senior commander in Kabul just before takeoff.

Mr. Williams wandered over. He sat down, picked up the briefing slides and maps. He paused before speaking.

Let me get this right, he said. We went into Afghanistan because Al Qaeda was in Afghanistan. All right. Al Qaeda is no longer in Afghanistan. All right. Al Qaeda is now over here in Pakistan. And we’re still fighting over here in Afghanistan?

No joke. His improvised analysis anticipated a heated policy debate about the war back in Washington.

Mr. Williams would open every routine in the war zone with a battle cry of “G-o-o-o-o-d morning, I-raq!” (or Af-ghanistan!), drawing on his portrayal of Adrian Cronauer, the military D.J. who spoke to and for the American troops in the film “Good Morning, Vietnam.”

Rear Adm. Frank Thorp IV, now retired, worked with Mr. Williams while serving as press adviser to the chairman of the Joint Chiefs of Staff and, after leaving active duty, during a tour as senior vice president at the U.S.O.

“No one was more supportive of the troops,” Admiral Thorp said this week. “And none of them knew that he was against the war. He was so very human and humble.”

Admiral Thorp recalled that Mr. Williams would “politely, and quickly” end conversations with senior generals when he saw young enlisted personnel coming his way.

“He brought the love and laughter of home to our troops in such a difficult time in their lives,” Admiral Thorp said. “And he expected nothing back. ”