It is ironic that a new book hit the market this past week that makes it very clear the president may be technically correct, but in real terms there probably are thousands of men and women, mostly Americans, who are in combat conditions in Iraq and elsewhere but they don’t wear the uniforms of the U.S. Army, Marines, SEALS, Air Force or Navy.

They are fighting in many ways, and most of the fighters are getting paid for their services by U.S. taxpayers.

These forces are part of the growing numbers of PMCs (private military companies) or PMSCs (private military and securities companies) that are on call, ready to perform any service at any time and at any place — places our formal military forces are unable to reach in time, places where they do not want to perform and places where they do not want the forces to be identified as American. In past years such fighters were called mercenaries.

They are effective, can be deadly and can perform many services that are helpful to this country.

The new book is titled “The Invisible Soldiers: How America Outsources our Security.” The author, Ann Hagedorn, was a Kansas University librarian at one time, a staff writer for the Wall Street Journal, a teacher at Northwestern and Columbia universities and was a fellow at KU’s Hall Center for the Humanities.

The book, likely to be a best-seller, is sure to cause a firestorm.

Hagedorn has done a masterful job in researching the business of the PMSCs, whether it is dealing with counter-terrorism actions and strategy, private security, the protection of embassies, working in kidnapping and ransom cases, fighting or supporting coup efforts, managing drone surveillance and missile strikes, maritime security and most any other tough, usually unpleasant task.

Hagedorn emphasizes she neither favors nor opposes the use and role of PMSCs and notes that they can be of great assistance, but transparency and oversight are necessary. Their numbers are sure to grow, but this growth can and likely will bring about many changes in our formal military forces and strategy.

It’s a huge business, growing month by month, if not day by day, as they are ready to spring into action whenever they get a call and someone is willing to pay the bills.

As Hagedorn points out, it is easier with fewer, if any, government approvals or delaying paperwork to call a PMSC company and ask it to get a job done. No worries about health and medical insurance, training expenses, family-assistance programs, thousands of idle forces when there is no battle to fight, or medical care after a military career. Just hire and fire them as jobs require.

A unique facet of using PMSCs is that it removes Washington and the public from direct involvement in an ugly or deadly action because PMSCs’ missions are multilayered with PMSCs often subcontracting various parts of the task they were hired to accomplish. Sometimes there may be up to five levels of sub-contractors. This provides a major detachment from or mental involvement in the actual conflict.

The on-call services are efficient and effective, but what are the problems created by this fast-growing business? There are definite consequences for our traditional forces. Who should govern or control the actions of these companies, which now are international?

“The Invisible Soldiers” could not be timelier; it is balanced, thorough and fair in its reporting. It is a phenomenon that is not going away, and the public needs to know how our government is relying on these businesses.

“The Invisible Soldiers” presents a very clear picture of the pros and cons and gives readers information to help decide why mercenaries or the dressed-up “invisible soldiers” may or may not be needed or used.

Hagedorn’s book should cause readers to ask themselves what happens if they, and the general public, do not become aware and concerned and seriously consider the pros and cons.

As she said at her Hall Center presentation, “Indifference is a serious threat to our society.”

While the helicopters may not arrive in time to help with the current fighting, the missiles are expected to be used by the Iraqi military in the battle to uproot Islamic fighters from Ramadi and Fallujah, cities that were the focus of major U.S. military operations during the height of the war in Iraq. When the U.S. begins sending the first batch of Apache helicopters and additional Hellfire missiles this year, more than 200 private defense-company personnel will be on hand.

They won't be alone.

Across Iraq, military specialists are helping the Iraqi military maintain its growing number of surveillance drones, attack helicopters and powerful missiles. Thousands more support the U.S. government as security guards, analysts, drivers and cooks.

The strategic deployment of defense contractors in Iraq underscores the shifting security landscape as the U.S. downsizes its military presence around the world. With fewer than 200 American military personnel in Iraq, continued U.S. military support there relies increasingly on the presence of contractors.

The role for the military contractors, which has dwindled along with the U.S. presence in Iraq, could become more important in the coming months as the Iraqi government seeks billions more in international military support to combat a growing threat from Islamist militants.

Employees of Bell Helicopter, a unit of Textron Inc., TXT -1.37% are training Iraqi forces to fly and repair light attack helicopters stationed at a military base in the so-called Sunni Triangle northwest of Baghdad, where the Iraqi military is battling resurgent Islamist fighters..

Two dozen Lockheed employees are helping the Iraqi military keep their C-130 transport planes in the air. The company is also sending nearly 500 Hellfire missiles, which are being increasingly used in the fight against al Qaeda militants.

And more than a dozen employees with Beechcraft Corp. and General Atomics maintain a fleet of "Peace Dragon" surveillance airplanes used to track insurgent activity around the country.

The U.S. spent more than $200 billion on contractors in Iraq and Afghanistan over the past decade as its reliance on private support grew, according to congressional estimates. In all, more than 5,000 contractors now work in Iraq as intelligence analysts, security guards, military trainers, translators and cooks.

"You have a situation where the government has become dependent on contractors," said Allison Stanger, a political-science professor at Middlebury College. "It's a real quantum shift."

Most U.S. contractors working in Iraq are unlikely to get involved in direct military operations. Along with U.S. legal restrictions on civilians engaging in combat, foreign military sales contracts often include provisions preventing contractors from being involved in direct combat, said Anthony Cordesman, a defense expert at the Center for Strategic and International Studies.

"Almost all of them will be protected from being asked to, or participating in, combat," Mr. Cordesman said. "You can't require anyone to have any kind of direct combat role."

Still, contractors serve in dangerous areas. In Afghanistan, more civilian contractors were being killed than U.S. soldiers by 2012, according to an analysis by Steven Schooner, a professor at George Washington University Law School. Now, he said, the traditional U.S. military role has been supplanted by civilians who are training and equipping the Iraqi military.

"The military task has, in fact, been outsourced in Iraq," he said.

The U.S. troop withdrawal from Iraq in 2011 brought the war to an official end. But the U.S. still retains a large presence at the embassy in Baghdad, which is still one of the biggest American diplomatic facilities in the world.

Over the past few years, the U.S. has been scaling back its presence in Iraq, and even the contractor force has dwindled.

As of January 2013, the U.S. had more than 12,500 contractors in Iraq, according to State Department and Pentagon figures. The U.S. has significantly reduced that number over the past year.

Of the roughly 5,000 contractors supporting the American diplomatic mission in Iraq, the State Department said, more than a third of them are U.S. citizens. They work for companies like Triple Canopy Inc., which provides security guards for U.S. diplomats, and L-3 Communications Holdings Inc., LLL -0.90% which helps the State Department vet Iraqis seeking jobs with the U.S. Many serve as cooks, translators and janitors.

Those numbers don't account for scores of military contractors working in Iraq as part of U.S.-approved foreign military sales that provide the Iraqi government with helicopters, missiles and other critical support.

U.S. lawmakers, led by Sen. Robert Menendez (D., N.J.), had blocked the Apache helicopter sale because of concerns that the Iraqi government would use them to crack down on minority groups.

Those concerns have now been allayed and the U.S. is stepping up its help as the Iraqi government tries to quash Sunni militants in Anbar province.