title: Gas attacks at Wulverghem
context: The Gas attacks at Wulverghem (30 April and 17 June 1916) were German cloud gas releases during the First World War on British troops in the municipality of Heuvelland, near Ypres in the Belgian province of West Flanders. The gas attacks were part of the sporadic fighting between battles in the Ypres Salient on the Western Front. The British Second Army held the ground from Messines Ridge northwards to Steenstraat and the divisions opposite the German XXIII Reserve Corps had received warnings of a gas attack. From 21 to 23 April, British artillery-fire exploded several gas cylinders in the German lines around Spanbroekmolen, which released greenish-yellow clouds. A gas alert was given on 25 April when the wind began to blow from the north-east and routine work was suspended; on 29 April, two German soldiers deserted and warned that an attack was imminent. Just after midnight on 30 April, the German attack began and over no man's land, a gas cloud drifted on the wind into the British defences, then south-west towards Bailleul.
question: When did the Gas attacks at Wulverghem take place?
answers: 30 April and 17 June 1916