Not long ago, a report surfaced on a Friday that a roadside bomb in Iraq had been hidden inside a dead dog. By the following Monday, the general who oversees the Army's training centers recalled, Army trainers back in the United States had copied the trick.

"It's a truly dynamic curriculum" at the training centers, changing as new tactics emerge in the fighting in Iraq, Lt. Gen. William S. Wallace said in an interview.

Fifteen months of combat in Iraq are leaving an imprint on the U.S. military. All the services are changing, but the Army especially is undergoing radical change as a result of the unexpectedly difficult occupation, in which it has suffered nearly 6,000 casualties.

The strain on Army troops, families and equipment has been extensively reported and is likely to intensify as some units head back to Iraq for a second tour. "The war in Iraq is wrecking the Army and the Marine Corps," retired Navy Capt. John Byron asserts in the July issue of Proceedings, the professional journal of Navy officers. "Troop rotations are in shambles and the all-volunteer force is starting to crumble as we extend combat tours and struggle to get enough boots on the ground."

The latest indication of the psychic toll was a recent study by the Walter Reed Army Institute of Research that found that about 16 percent of soldiers who have served in Iraq are showing signs of combat trauma.

Overall, "this kind of stress causes change -- some of it good, some of it not so good," said Sen. Jack Reed (D-R.I.), a former Army officer who serves on the Senate Armed Services Committee.

Indeed, other, less visible changes also are occurring -- and some of them are for the better. A generation of younger Army officers has been seasoned by a year of combat in a harsh and unpredictable environment, for example. And as the Army seeks to adjust to waging a counterinsurgency campaign 7,000 miles away, innovation in how it trains new recruits and structures forces for deployment is now rippling through the service.

"Iraq is accelerating the pace of change in the military -- the Army particularly," said retired Army Lt. Col. James Jay Carafano, a defense analyst at the Heritage Foundation. "It is forcing them to look at a lot of things they had pushed off because they were hard to do."

In the other services, the changes seem to be mainly financial. At the Navy's big East Coast base in Norfolk, fewer tugboats will be on call this summer to help steer warships to their berths, a result of a decision to tighten base budgets to free up $300 million to help pay for Navy and Marine operations in Iraq. The sea service also is deferring purchases of some spare parts until the new federal fiscal year begins, in October.

"There may be some degradation of readiness as a result," said Vice Adm. Cutler Dawson, deputy chief of naval operations for resources. He also said he thought the effect would be short-term.

At the Air Force, trims are being made in the budgets for travel, transfers, and some purchases of parts and supplies. "We're attempting to minimize any of the readiness impacts," said Maj. Gen. Steve Lorenz, the Air Force's budget director. "We won't know until the end of the year how it all shakes out."

There is no question that the Army personnel system is stressed. "I think the Army is in terrible shape," said retired Army Lt. Gen. Jay M. Garner, who served last year as the Bush administration's first administrator in postwar Iraq. "I think people are worn out, equipment is run down and we've overstressed the reserves. We're drastically short [of] infantry and MPs because the Army is too small."

Other experts worry about the hidden costs of using up equipment in the extreme heat and abrasive dust of Iraq. Helicopters, armored vehicles and Humvees will have shorter service lives than the Army planned. "Equipment's taking a beating. Aircraft and high-cost tank engines are accumulating lots of hours," said retired Army Lt. Gen. Leonard Holder.

In the Army, the biggest long-term changes may be in how it trains -- if the lessons learned in counterinsurgency stick. After the Vietnam War, noted retired Army Lt. Col. Andrew F. Krepinevich Jr., who wrote a book on the Army and Vietnam, "we got out of the counterinsurgency business."

Historically, the National Training Center, the Army's premier combat training facility, has focused on simulating combat between tank-heavy mechanized forces in open, high-desert terrain. But over the past year, it has added urban areas, hired some Iraqi Americans to work in them and interact with troops, and even put caves up in the hills where those playing opposing guerrilla forces can hide weapons and other supplies.

If Army soldiers treat the "locals" well in the urban areas, they learn more about those weapons caches. If they don't, they find out about the weapons the hard way. New training scenarios also require Army commanders to handle everything from combat operations to refugee relief simultaneously.

The Army also has added 8,000 slots to the normally 25,000 infantrymen it trains annually at Fort Benning, Ga. To handle the surge, and to replace drill sergeants deployed to Iraq and Afghanistan to train locals there, it has mobilized about 100 reservists to drill the new soldiers.

Even mechanics and clerks now are given training in combat operations, such as defending a convoy or reacting to an ambush, said Bob Seger, acting deputy chief of staff for operations at the Army's Training and Doctrine Command. "This is introductory training for everybody, not just infantry or cavalry scouts," he said. "From initial entry training of soldiers all the way up to general officers, we are designing new courses and doing everything we can to get people ready to go."

Wallace, who is head of the Army's Combined Arms Center, said the changes in Army training are the most significant since the "training revolution" of the early 1980s, when the service came out of its post-Vietnam funk and based its training on realistic mock combat against a professional opposing force with trained observers.

Not everyone is as sanguine. Army insiders report quiet worry in the service about the recent decision to deploy to Iraq the opposing forces from two of the Army's three major training centers. "To move our best trainers to the combat zone proves to you how stretched the Army is," said retired Army Col. John Antal.

Moves like that indicate that the service may be eating its seed corn. "We need to keep our eye on this," said one senior Army general, who worries about the possibility of keeping tens of thousands of troops in Iraq for years. "We'll survive in the short term, but we have to be careful not to inadvertently cut our collective throat in the long term."

The greatest long-term effect of the difficult environment in Iraq may be on the generation of younger officers and soldiers who have led platoons and companies there over the past year. "The complexity, unpredictability and ambiguity of postwar Iraq is producing a cohort of innovative, confident and adaptable junior officers," said retired Army Lt. Col. Leonard Wong, an expert in military personnel issues.

Wong has just completed for the Army War College a study for which he interviewed more than 50 lieutenants and captains serving in Iraq. His conclusion: "Our troops aren't just competent; Iraq also is teaching them capacity -- they can handle a lot more. With all the incredibly bad-news stories you hear out of Operation Iraqi Freedom, this is a good-news story -- if we leverage it correctly."

His concern, he said, is that the Army will not know what to do with those agile, intellectually creative officers, and on their return will simply put them back into the lockstep of garrison life, rather than seek to find ways to nurture their newfound skills. One captain who recently returned from a year of combat in Iraq noted that he was returned to "restrictive training limitations of the past era," making it more difficult to convey some of the hard-earned knowledge he brought back.

But retired Col. Douglas Macgregor, who left the Army last month, has a darker view of the choices those younger officers are likely to make. He said he believes that the situation in Iraq is such a mess, with the Army pursuing "wrongheaded tactics," that, "in the end, our best soldiers, sergeants, lieutenants and captains will leave in disgust, and we will be unprepared for the future regional Middle Eastern war that our weak performance in Iraq now makes inevitable."