On the naval front, the Ottoman fleet twice exited the Dardanelles and was twice defeated by the Greek Navy, in the battles of Elli and Lemnos. Greek dominance on the Aegean Sea made it impossible for the Ottomans to transfer the planned troops from the Middle East to the Thracian (against the Bulgarian) and to the Macedonian (against the Greeks and Serbians) fronts. According to E.J. Erickson the Greek Navy also played a crucial, albeit indirect role, in the Thracian campaign by neutralizing no less than three Thracian Corps (see First Balkan War, the Bulgarian theater of operations), a significant portion of the Ottoman Army there, in the all-important opening round of the war. After the defeat of the Ottoman fleet, the Greek Navy was also free to liberate the islands of the Aegean. General Nikola Ivanov identified the activity of the Greek Navy as the chief factor in the general success of the allies.