Members of the Coalition included Australia: 2,000 invasion, Poland: 200 invasion—2,500 peak, United Kingdom: 46,000 invasion, United States: 150,000 to 250,000 invasion

United Kingdom

British troops, in what was codenamed Operation (or Op) TELIC participated in the 2003 Invasion of Iraq. The 1st Armoured Division was deployed to the Gulf and commanded British forces in the area, securing areas in southern Iraq, including the city of Basra during the invasion. A total of 46,000 troops of all the British Services were committed to the operation at its start. Including were some 5,000 Royal Navy and Royal Fleet Auxiliary sailors and 4,000 Royal Marines, 26,000 British Army soldiers, and 8,100 Royal Air Force airmen.

Polish

The Battle of Umm Qasr was the first military confrontation in the Iraq War, with its objective the capture of the port.Polish GROM troops supported the amphibious assault on Umm Qasrby with the British 3 Commando Brigade of the Royal Marines, and the US 15th Marine Expeditionary Unit. After the waterway was de-mined by a Detachment from HM-14 and Naval Special Clearance Team ONE of the U.S. Navy and reopened, Umm Qasr played an important role in the shipment of humanitarian supplies to Iraqi civilians.

Australia

Australia contributed approximately 2,000 ADF personnel, including a special forces task group, three warships and 14 F/A-18 Hornet aircraft.

Summary of the invasion

The US-led Coalition forces toppled the government and captured the key cities of a large nation in only 21 days. The invasion did require a large army build-up like the 1991 Gulf War, but many didn't see combat and many were withdrawn after the invasion ended. This proved to be short-sighted, however, due to the requirement for a much larger force to combat the irregular Iraqi forces in the aftermath of the war. General Eric Shinseki, Army Chief of Staff, recommended "several hundred thousand" troops be used to maintain post-war order, but then Secretary of Defense Donald Rumsfeld—and especially his deputy, civilian Paul Wolfowitz—strongly disagreed. General Abizaid later said General Shinseki had been right.

The Iraqi army, armed mainly with Soviet-built equipment, was overall ill-equipped in comparison to the U.S. and UK forces. Attacks on U.S. supply routes by Fedayeen militiamen were repulsed. The Iraqis' artillery proved largely ineffective, and they were unable to mobilize their air force to attempt a defense. The Iraqi T-72 tanks, the heaviest armored vehicles in the Iraqi Army, were both outdated and ill-maintained, and when they were mobilized they were rapidly destroyed, thanks in part to U.S. and UK air supremacy. The U.S. Air Force, Marine Corps, Naval Aviation, and British Royal Air Force operated with impunity throughout the country, pinpointing heavily defended resistance targets and destroying them before ground troops arrived.

The main battle tanks (MBT) of the U.S. and UK forces, the U.S. M1 Abrams and British Challenger 2, proved worthy in the rapid advance across the country. With the large number of rocket propelled grenade (RPG) attacks by irregular Iraqi forces, few U.S. and UK tanks were lost and no tank crew were killed by hostile fire. The only tank loss sustained by the British Army was a Challenger 2 of the Queen's Royal Lancers that was hit by another Challenger 2, killing two crew members. All three British tank crew fatalities were a result of friendly fire.

The Iraqi Army suffered from poor morale, even amongst the elite Republican Guard. Entire units disbanded into the crowds upon the approach of invading troops, or actually sought out U.S. and UK forces out to surrender. In one case, a force of roughly 20–30 Iraqis attempted to surrender to a two-man vehicle repair and recovery team, invoking similar instances of Iraqis surrendering to news crews during the Persian Gulf War. Other Iraqi Army officers were bribed by the Central Intelligence Agency (CIA) or coerced into surrendering.

Worse, the Iraqi Army had incompetent leadership – reports state that Qusay Hussein, charged with the defense of Baghdad, dramatically shifted the positions of the two main divisions protecting Baghdad several times in the days before the arrival of U.S. forces, and as a result the units within were both confused and further demoralized when U.S. Army forces attacked. The invasion force did not see the entire Iraqi military thrown against it; U.S. and UK units had orders to move to and seize objective target-points rather than seek engagements with Iraqi units. This resulted in most regular Iraqi military units emerging from the war fully intact and without ever having been engaged by U.S. forces, especially in southern Iraq. It is assumed that most units disintegrated to either join the growing Iraqi insurgency or returned to their homes.

According to the declassified Pentagon report, "The largest contributing factor to the complete defeat of Iraq's military forces was the continued interference by Saddam." The report, designed to help U.S. officials understand in hindsight how Saddam and his military commanders prepared for and fought the invasion, paints a picture of an Iraqi government blind to the threat it faced, hampered by Saddam's inept military leadership and deceived by its own propaganda and inability to believe the United States would invade a sovereign country without provocation. According to the BBC, the report portrays Saddam Hussein as "chronically out of touch with reality - preoccupied with the prevention of domestic unrest and with the threat posed by Iran."

Security, looting and war damage

Looting took place in the days following the 2003 invasion of Iraq.

It was reported that the National Museum of Iraq was among the looted sites. Most initial news reports were that 100 percent of the museum's artifacts had been removed by looters. In fact, no more than 3 percent of its contents were removed by thieves.

An assertion that U.S. forces did not guard the museum because they were guarding the Ministry of Oil and Ministry of Interior is disputed by investigator Colonel Matthew Bogdanos in his 2005 book, "Thieves of Baghdad." Bogdanos notes that the Ministry of Oil building was bombed, but the museum complex, which took some fire, was not bombed. He also writes that Saddam Hussein's troops set up sniper's nests inside and on top of the museum, and nevertheless U.S. Marines and soldiers stayed close enough to prevent wholesale looting.

Early on, U.S. officials reacted defensively to the first, false news reports of 100 percent looting. According to U.S. officials, the "reality of the situation on the ground" was that hospitals, water plants, and ministries with vital intelligence needed security more than other sites. There were only enough U.S. troops on the ground to guard a certain number of the many sites that ideally needed protection, and so, apparently, some "hard choices" were made.

The FBI was soon called into Iraq to track down the stolen items. It was found that the initial claims of looting of substantial portions of the collection were heavily exaggerated. Initial reports claimed a near-total looting of the museum, estimated at upwards of 170,000 inventory lots, or about 501,000 pieces. The most recent estimate places the number of stolen pieces at around 15,000, and about 10,000 of them probably were taken in an "inside job" before U.S. troops arrived, according to Bogdanos. Over 5,000 looted items have since been recovered.

There has been speculation that some objects still missing were not taken by looters during the invasion, but were taken by Saddam Hussein or his government before or during the fighting. There have also been reports that early looters had keys to vaults that held rarer pieces, and some have speculated as to the pre-meditated systematic removal of key artifacts.

The National Museum of Iraq was only one of many museums and sites of cultural significance that were affected by the war. Many in the arts and antiquities communities briefed policy makers before the need to secure Iraqi museums. Despite the looting being lighter than initially feared, the cultural loss of items from ancient Sumer is significant.

More serious for the post-war state of Iraq was the looting of cached weaponry and ordnance which fueled the subsequent insurgency. As many as 250,000 tons of explosives were unaccounted for by October 2004. Disputes within the US Defense Department led to delays in the post-invasion assessment and protection of Iraqi nuclear facilities. Tuwaitha, the Iraqi site most scrutinized by UN inspectors since 1991, was left unguarded and was looted.

Zainab Bahrani, professor of Ancient Near Eastern Art History and Archaeology at Columbia University, reported that a helicopter landing pad was constructed in the heart of the ancient city of Babylon, and "removed layers of archeological earth from the site. The daily flights of the helicopters rattle the ancient walls and the winds created by their rotors blast sand against the fragile bricks. When my colleague at the site, Maryam Moussa, and I asked military personnel in charge that the helipad be shut down, the response was that it had to remain open for security reasons, for the safety of the troops."

Bahrani also reported that in the summer of 2004, "the wall of the Temple of Nabu and the roof of the Temple of Ninmah, both sixth century BC, collapsed as a result of the movement of helicopters." Electrical power is scarce in post-war Iraq, Bahrani reported, and some fragile artifacts, including the Ottoman Archive, would not survive the loss of refrigeration.

Bush declares "End of major combat operations" (May 2003)

On May 1, 2003, Bush landed on the aircraft carrier USS Abraham Lincoln, in a Lockheed S-3 Viking, where he gave a speech announcing the end of major combat operations in the Iraq war. Bush's landing was criticized by opponents as an unnecessarily theatrical and expensive stunt. Clearly visible in the background was a banner stating "Mission Accomplished." The banner, made by White House staff and supplied by request of the United States Navy, was criticized as premature. The White House subsequently released a statement that the sign and Bush's visit referred to the initial invasion of Iraq and disputing the claim of theatrics. The speech itself noted: "We have difficult work to do in Iraq. We are bringing order to parts of that country that remain dangerous."

Post-invasion Iraq has been marked by violent conflict between U.S.-led soldiers and insurgents. The ongoing resistance in Iraq was concentrated in, but not limited to, an area referred to as the Sunni triangle and Baghdad.

This resistance may be described as guerrilla warfare. The tactics in use were to include mortars, suicide bombers, roadside bombs, small arms fire, improvised explosive devices (IED's), and handheld antitank grenade-launchers (RPG's), as well as sabotage against the oil infrastructure. There were also attacks toward the power and water infrastructure.

There is evidence that some of the resistance was organized, perhaps by the fedayeen and other Saddam Hussein or Ba'ath loyalists, religious radicals, Iraqis angered by the occupation, and foreign fighters.