Amid the media frenzy over former CIA director David Petraeus’ extramarital affair, we were struck by a quick reference in a Washington Post story about Petraeus’ time running the war in Afghanistan:

Prominent members of conservative, Washington-based defense think tanks were given permanent office space at his headquarters and access to military aircraft to tour the battlefield. They provided advice to field commanders that sometimes conflicted with orders the commanders were getting from their immediate bosses.

So who were these think-tankers and what exactly were they doing?

We spoke to some of them.

The most prominent and frequent traveler appears to have been the American Enterprise Institute’s Fred Kagan. Best known as the intellectual author of the Iraq surge strategy, Kagan said he and his wife, Kimberley Kagan of the Institute for the Study of War, spent a total of about 270 days in Afghanistan while Petraeus was in command from summer 2010 to summer 2011, and about 128 days under Gen. John Allen, who took command after Petraeus and remains in the position.

Like others we spoke with, Kagan said Petraeus and other generals have routinely brought think tankers to both Iraq and Afghanistan, both to solicit outside advice and to shape the debate back home.

“General Petraeus liked to talk about ‘directed telescopes’ to describe people who go down to lower echelons and see what’s going on and go back and help the commander get a better sense of that,” says Kagan, who added that he has been going on such trips since 2007. The other aim of the trips was for the military to “help inform people who were going to be writing in the national debate to understand what was going on on the ground.”

Responding to the Post’s characterization about the military resources made available to think tank members during Petraeus’ time in charge in Afghanistan, Kagan said: “Everybody who travels to Afghanistan or any combat zone at the invitation of the military is given access to military aircraft.”

On the issue of providing advice to field commanders that conflicted with advice of their bosses, Kagan said: “We were always very careful to say we are not giving you orders, we’re not passing on orders. We’re not doing anything except giving you our opinion.”

Defense Department spokesman Bill Speaks told ProPublica that the Pentagon often reaches out to such outside experts to advise war commanders.

“We do periodically invite those experts involved in relevant research to receive briefings on the status of the campaign,” Speaks said in an email. He said the military does not have a comprehensive list of think tank members who have visited the U.S. headquarters in Kabul.

Indeed, the trips do not appear to have been part of any formal program, and they often differed in length and purpose.

Other think tankers we spoke with say they spent much less time in Afghanistan than Kagan, usually a few weeks or less. Those who have participated are from both Republican- and Democratic-leaning think tanks and they said they were not compensated.

“We did battlefield circulation, visited units in the field, and met with local political and security leaders,” says John Nagl, a retired Army officer and current fellow at the Center for a New American Security who took one military trip to Iraq and two to Afghanistan.

Nagl — who said attendees were responsible for getting to Kabul on their own and the military then covered transportation, lodging, and food — believed the trips allowed him “to be better informed in my analysis and advocacy.”

Michael O’Hanlon of the Brookings Institution, who has taken the trips several times to both Iraq and Afghanistan, says the practice first became common under Petraeus during the surge in Iraq in 2007.

Kenneth Pollack, also of Brookings, credits a 2007 military trip to Iraq with prompting him and O’Hanlon to write an influential New York Times op-ed supporting Petraeus’ surge strategy in the country.

“I hesitate to say these trips are uniformly good or bad. They can be both, they can be neither,” Pollack told us.  “It so depends on the people you meet and the people you’re taking” on the trip.  At times “there’s no question they’re trying to have you see things the way that they see them. But if you’re smart about it, you can get past that.”

Max Boot, a fellow at the Council on Foreign Relations, has also gone on the trips. He declined to comment.