A number of problems with Patriot missile (search) defenses and related systems contributed to three friendly fire deaths during the U.S.-led invasion of Iraq, according to a new Pentagon report, which nonetheless says the Patriot was a "substantial success" during the fighting.

Patriots appear to have shot down nine incoming Iraqi short-range ballistic missiles (search) during the invasion, says a summary of the report.

But Patriot batteries also misidentified and shot down an American and a British fighter in separate incidents, leaving three air crew members dead. A Patriot system also mistakenly tracked another U.S. fighter, which bombed a radar in response. The incidents took place in March and April 2003.

The report, posted on a military Web site this week, was authored by a task force of the Defense Science Board, which advises Secretary of Defense Donald H. Rumsfeld (search) on a range of issues.

In general, the report attributes he friendly fire incidents to the technical difficulty of tracking a single incoming missile among the hundreds of friendly aircraft that flew sorties during the early part of the war. Specifically, it pointed to three shortfalls:

—Well-known, but still uncorrected, problems with a system called IFF, for "identification friend or foe," that aircraft carry to identify them to American and allied systems as friendly. Patriots should be restricted from firing at aircraft broadcasting a friendly signal, but the shoot-down of the British aircraft in particular was blamed on faulty IFF.

"This is not exactly a surprise; this poor performance has been seen in many training exercises. The Task Force (that authored the report) remains puzzled as to why this deficiency never garners enough resolve and support to result in a robust fix," the report says.

—Overall problems with the ability of missile defense systems and other ground-based and airborne radars to pass information to one another, which leaves Patriot crew members in the dark about the total picture in the skies.

"The communication links, the ability to correlate target tracks by disparate sensors, and the overall information architecture are simply not there. Thus, a Patriot battery on the battlefield can be very much alone," the report says.

—An over-reliance by crew members and commanders on Patriot computers, rather than their own intuition. Patriot crews are trained for situations where they face a rain of missiles, not one filled with a few missiles mixed in among friendly aircraft.

Previously, U.S. Central Command officials said Patriots downed at least 10 of the 17 missiles fired at Kuwait. Why the Pentagon report claims one less missile was killed is unclear, although it says that all nine missiles that entered an area protected by Patriots were shot down.

"In an overall sense, the Task Force assessed the Patriot missile defense in (Operation Iraqi Freedom) to be a substantial success," the report says.

During the 1991 Gulf War, the military and Raytheon, the Patriot's manufacturer, claimed high success — up to 80 percent — with earlier versions of the Patriot. Congress' General Accounting Office later found Patriots intercepted no more than four of 47 Iraqi Scud missiles, a 9 percent success rate. The Pentagon has spent more than $3 billion improving the Patriots since then.