1915: February 19
The Gallipoli campaign to take control of the narrow sea route that separated Europe from Asia in the north-west of what is now Turkey began in February 1915. The Allies saw the straits as having strategic value; it gave access to the Ottoman capital Constantinople and provided a route to the Black Sea and therefore a supply route to Allied Russia.
It was Winston Churchill who proposed the naval-based attack that was launched on February 19. A combination of British and French battleships began a long-range bombardment of the Ottoman coast but their weak fire power proved ineffective against the solid Ottoman resistance and natural geographic defences. Largely unsuccessful Allied campaigns continued over the following two months until March 8 when one disastrous attempt led to three ships being sunk and another three damaged by Ottoman mines.
The mission was eventually abandoned and a land invasion of 120,000 troops was ordered for April 25. The results were devastating. The Ottoman defence pushed the Allies back, trenches were dug and a bloody stalemate followed. Over the coming months around 250,000 Allied troops, including many soldiers from Australia and New Zealand, died at Gallipoli. Ottoman casualties were roughly the same. Having failed to make any progress the last Allied soldiers finally left the region in January 1916 and Churchill resigned from his post as First Lord of the Admiralty.