By April 1941 Greece had defeated the Italian invasion and was therefore Britain's only effective ally in Europe. British leaders, especially Winston Churchill, the British Prime Minister, thought it was politically unacceptable not to support an ally under threat. In addition, use of Greek airfields would put the Romanian oilfields at Ploieşti, vital to Germany's war effort, within reach of Allied bombers. GeneralArchibald Wavell, commander of all the Allied forces in the Middle East, was told in January 1941 that support for Greece must take precedence over all operations in North Africa and this order was reinforced in February. Wavell's attitude is unclear. It had been generally believed that he was pushed into the Greek campaign, but recent writers believe that Wavell approved of it. British commanders concluded that with British help, the Greek Army could hold the Germans at the Aliakmon Line. They knew German forces were being sent to Libya in Operation Sonnenblume, but thought these forces would be ineffectual until the summer. However, it is now accepted that given the disposition of Greek forces the transfer of further Allied forces to the Greek mainland had no chance of preventing a German victory there, as well as weakening Allied forces in North Africa, leading to the success of Rommel's counterattack in April and the failure of an Allied offensive, Operation Brevity, in May. From 4 March, a series of convoys moved from Alexandria to Piraeus at regular 3-day intervals, escorted by warships of the Royal Navy and the Royal Australian Navy. Although there were air attacks, these had little effect. Since January, when the Italian torpedo boats Lupo and Libraattacked convoy AN 14 off Suda bay and disabled the large tanker Desmoulea for the rest of the war, Allied shipping used to avoid passage into the Aegean Sea through the Kaso strait and chose the Antikithera strait instead, which was west of Crete. The Italian fleet mounted a major attempt at the end of March to disrupt these convoys south of the island, but it ended in the stunning defeat at Cape Matapan. The Allies initially planned to deploy about 58,000 personnel and their equipment to Greece by 2 April, including the British 1st Armoured Brigade, the New Zealand 2nd Division and the Australian 6th Division. While it was intended that these units would be followed by the Australian 7th Division and the Polish Independent Carpathian Rifle Brigade, neither was deployed before the defeat of the Allies on the Greek mainland. Two infantry and two armored divisions were in place on the Aliakmon Line, south-west of Thessaloniki, before the Axis invasion on 6 April. The Greek Army did not retire to the Aliakmon Line as expected for fear of being overrun by the more mobile German troops during a retirement and the Allied troops were left vulnerable. These forces had little effect on the German invasion and they were evacuated on and after 24 April. Some of these units were moved to Crete, where they were defeated and forced to evacuate by the airborne invasion of that island.
