It was 18th of march, the day an important (and failed) offensive against Turkey in WW 1 was commemorated.
From the Wikipedia (caption Çanakkale): On 19 February, the first attack on the Dardanelles began when a strong Anglo-French task force, including the British battleship HMS Queen Elizabeth, bombarded Turkish artillery along the coast.
A new attack was launched on 18 March, targeted at the narrowest point of the Dardanelles where the straits are just a mile wide. A massive fleet under the command of Admiral de Robeck containing no fewer than 16 battleships tried to advance through the Dardanelles. However almost every ship was damaged by sea mines which were laid along the Asian shore by the Turkish minelayer Nusrat. Trawlermen had been used by the British as minesweepers, but they retreated as the Turks opened fire on them, leaving the minefields intact. Soon afterwards three battleships were sunk (HMS Ocean and HMS Irresistible and the French Bouvet), while the battlecruiser HMS Inflexible and the French battleships Suffren and Gaulois were badly damaged.