Greek Summer Offensive The Greek Summer Offensive 1920 was an offensive by the Greek army , assisted by British forces , to capture the southern region of the Sea of Marmara and the Aegean Region . Additionally they were supported by the Kuva - i Inzibatiye of the Ottoman government in Constantinople . The Kuva - i Inzibatiye was created to crush any Turkish resistance forces . This offensive was one of several engagements where British troops assisted the advancing Greek army . British troops actively took part in invading coastal towns of the Sea of Marmara . With the approval of the Allies , the Greeks started their offensive on 22 June 1920 and crossed the ' Milne Line ' . The ' Milne Line ' was the demarcation line between Greece and Turkey , laid down in Paris . Resistance by the Turks was limited , as they had few and ill - equipped troops in western Anatolia . They were also busy on the eastern and southern fronts with their limited number of troops . After offering some opposition , they retreated to Eskişehir on Mustafa Kemal Pasha ' s order . Prelude . In May 1920 the Kuva - i Inzibatiye , backed by the British , had been sent to seize the area of Geyve and İzmit , but they were repelled by the Turkish irregular forces . Subsequently British aeroplanes bombed the Turkish positions in İzmit with little outcome . 3 regiments from the Kuva - i Inzibatiye entrenched themselves at the outsirts of İzmit . Behind them were 2 - 3 British battalion s and furthermore they were backed up by several British battleship s from the sea . On 15 June , the Turks tried to advance towards the Ottoman and British positions , but they made little progress , as British battleship s and planes started to bomb them on 16 – 17 June . On this occasion , the British 15 inch naval guns saw their first action by bombing Turkish positions . Offensive . The situation was a stalemate , therefore the British decided to bring in the Greek army for assistance and to punish the attacks on their troops . The Greeks , meanwhile , were eager to conquer their historical homeland . The British military staff together with the Greek military staff planned the offensive for the southern coastal area of the Sea of Marmara and the Aegean Region . With these plans the Greek army started its offensive on 22 June 1920 . During the offensive , British and Greek troops jointly captured the following towns , some of these towns were invaded by naval landing forces : Akhisar ( 22 June ) ; Kırkağaç , Soma and Salihli ( 24 June ) ; Alaşehir ( 25 June ) ; Kula ( 28 June ) ; Balıkesir ( 30 June ) ; Bandırma , Kırmesti and Karacabey ( 2 July ) ; Nazilli ( 3 July ) ; Gemlik and Mudanya ( 6 July ) ; Bursa ( 8 July ) ; Karamürsel ( 11 July ) ; İznik ( 12 July ) ; Gediz and Ulubey ( 28 August ) ; Uşak ( 29 August ) ; Simav ( 3 September ) . During the offensive against these areas , several clashes occurred between the advancing British - Greek troops and the defending Turkish irregular forces . For example Mudanya had been tried to be captured as early as 25 June by naval landing forces , but stubborn Turkish resistance inflicted casualties on British forces and forced them to withdraw . On 6 July a British fleet of 12 ships bombed the town for three hours which killed 25 Turkish soldiers during the bombardment . After the bombardment British troops landed and took control control of the town . There were many instances of successful delaying operations of small Turkish irregular forces against numerical superior enemy troops . Such as in Savaştepe when a Turkish irregular unit of 200 men delayed a Greek division of 10 , 000 men for one day . By reaching Uşak on 29 June , the Greek army had advanced some 125 miles ( 200 km ) . Apart from these major settlements , several other smaller settlement s were captured during the offensive . Aftermath . The Turks started a small counter - attack in the area of Gediz , but it had limited success .