アングロ＝イラク戦争
Air Vice-Marshal Smart controlled a base with a population of around 9,000 civilians that was indefensible with the force of roughly 2,500 men currently available. The 2,500 men included air crew and Assyrian Levies, who were prized by the British for their loyalty, discipline and fighting qualities. There was also the possibility that the Iraqi rebels were waiting for dark before attacking. As a result, Air Vice-Marshal Smart decided to accept the tactical risks and stick to Middle East Command's policy of avoiding aggravation in Iraq by, for the moment, not launching a pre-emptive strike.
Late on 6 May, the Iraqis besieging Habbaniya pulled out. By dawn on Wednesday 7 May, RAF armoured cars reconnoitred the top of the escarpment and reported it to be deserted. The Iraqi force had abandoned substantial quantities of arms and equipment; the British garrison gained six Czechoslovakian-built 3.7 inch howitzers along with 2,400 shells, one 18-pounder gun, one Italian tank, ten Crossley armoured cars, 79 trucks, three 20 mm anti-aircraft guns with 2,500 shells, 45 Bren light machine-guns, eleven Vickers machine guns, and 340 rifles with 500,000 rounds of ammunition.
The investment of Habbaniya, by Iraqi forces, had come to an end.
On 30 May, the 10th Indian Infantry Division's third brigade, 25th Indian Infantry Brigade under Brigadier Ronald Mountain, arrived and disembarked at Basra. The 25th Indian Infantry Brigade included 3rd battalion 9th Jat Regiment, 2nd battalion 11th Royal Sikh Regiment, and 1st battalion 5th Mahratta Light Infantry. In June 1941, additional British forces arrived in Basra from India. On 9 June, the 17th Indian Infantry Brigade arrived and, on 16 June, the 24th Indian Infantry Brigade arrived.
The force put together in Palestine by Wavell was codenamed Habforce, short for Habbaniya Force. The force was placed under the command of Major-General George Clark, who was the commander of the 1st Cavalry Division. After Wavell complained that using any of the force stationed in Palestine for service in Iraq would put Palestine and Egypt at risk, Churchill wrote Hastings Ismay, Secretary of the Chiefs-of-Staff Committee, and asked: "Why would the force mentioned, which seems considerable, be deemed insufficient to deal with the Iraq Army?" Concerning the 1st Cavalry Division specifically, he wrote: "Fancy having kept the cavalry division in Palestine all this time without having the rudiments of a mobile column organised!" On balance, Wavell wrote that the 1st Cavalry Division in Palestine had been stripped of its artillery, its engineers, its signals, and its transport to provide for the needs of other formations in Greece, North Africa, and East Africa.
1932年の独立まで、イラクは国際連盟のイギリス委任統治領メソポタミアとなっていた。独立前の1930年、イギリスは、イラク国内でイギリス軍の軍事通行権、軍事基地の使用および建設の権利を認めさせる条約を、イラク国内での反感を買いながら締結したことがあった。
独立後の1937年には、すでにイラク国内から多くのイギリス軍が撤退し、イラクは国内の安全を確保できる軍事力を持つようになった。この頃もイギリス空軍(RAF)は基地の利用を許可されていたが、その権限も、バスラ近郊のシャイバ基地、ファルージャとラマディの間にあるハバニヤ基地(イラクのイギリス空軍将校のH・G・スマートの指揮下)の二つに限られていた。とはいえ、この基地は英領エジプトから英領インドの空路にとっても、イギリスの石油権益にも重要な存在だった(ハバニヤは、バグダードの東にある)。
第二次世界大戦の開戦時、ハバニヤ基地は、イギリスの第一装甲車中隊と地元の徴兵部隊の訓練基地となった。
1939年9月、ポーランド侵攻を受けてイラク政府はナチス・ドイツとの国交を断絶したが、翌年3月、これに反発する国粋主義者のラシッド・アリが首相となった。アリは公式には枢軸国を支持していないように見せるために、密かにドイツと連絡を取っていたが、6月に枢軸国として第二次世界大戦に参戦したファシストのイタリア王国とは国交を続け、イタリア軍を反英プロパガンダに利用し、イギリス領パレスチナから亡命した大ムフティーのアミーン・フセイニもこの活動を支援した。しかし、結果的に起こった混乱と内戦の可能性が原因で、1941年1月に、アリは首相を辞任し、タハ・アル・ハシミ(英語版)が後任となった。
C Company of the 1st Battalion The Essex Regiment were ordered to travel from Palestine to H4, between Haifa and Iraq; from here the company would join a detachment of RAF armoured cars and defend the position from the Iraqi rebels.
On 4 May, Churchill ordered Wavell to dispatch a force from Palestine. On 5 May, Wavell was placed in command of operations in northern Iraq and General Maitland Wilson was called back from Greece to take command of forces in Palestine and Transjordan. The Defence Committee and chiefs-of-staff rationale for taking military action against the Iraqi rebels was that they needed to secure the country from Axis intervention and considered Rashid Ali to have been conspiring with the Axis powers.