From late 1914, an Anglo-French naval force was assembled to force its way through the Dardanelles straits into the Sea of Marmara and to reach the Ottoman capital. The Allied planners knew that the Dardanelles and the Sea of Marmara was protected by coastal forts and naval forces. However, it was assumed (wrongly) that the defences would not be strong enough to prevent an Allied naval task force forcing its way through to Istanbul.
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Between November 1914 and March 1915, Allied warships repeatedly bombarded the Dardanelles forts. The initial attacks were intended to test the resolve of the Turkish defenders and to exhaust their reserves of artillery shells. The later attacks were intended to force their way through the last line of forts and clear the mine-fields protecting the entrance to the Sea of Marmara itself. On the 18 March, believing that the last mine-fields had been cleared, Vice Admiral SH Carden (the Allied Naval commander) ordered his battleships to take the lead in entering the Sea of Marmara. Unfortunately, the last mine-field was not cleared. Between 13.54pm and 18.05pm on the afternoon of 18 March, three pre-dreadnought battleships and one modern battle-cruiser were sunk; a further three battleships were damaged. Unwilling to accept such continuing losses, Carden ordered his forces to withdraw.
|Source: The War Illustrated, 1 May 1915.Image Source: File from Wiki Commons http://en.wikipedia.org/wiki/File:HMS_Irresistible_abandoned_18_March_1915.jpg
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Anglo-French naval forces remained in the Dardanelles throughout the campaign, bombarding the Turkish forts and providing naval gun-fire support to the later Allied land campaign. Allied submarines also entered the Sea of Marmara to harass Turkish shipping and gather intelligence. However Allied surface warships did not attempt again to push their way into the Sea of Marmara.