[Illustration: "Jeff" Phipps-Hornby and Frederic Coleman comparing underpinning outside Ypres, May, 1915; the thinnest and thickest "supports" in the 1st Cavalry Division] From the Zonnebeke Road south, across the Ypres-Roulers Railway, as far as the Bellewaarde Lake, troops of the 28th Division composed the firing line. They joined the left flank of the 18th Hussars, who occupied a position on the south side of the Bellewaarde Lake and in front of the Hooge Château, the trenches at that point being about thirty yards to the east of the château ruins. The right of the 18th Hussars rested on the Menin Road, and close behind them in reserve were three score odd York and Durham Tommies who had been sent up to dig. South of the Menin Road, in the Sanctuary Wood, came the 9th Lancers, 11th Hussars, Queen's Bays, and 5th Dragoon Guards, respectively. The 4th Dragoon Guards, 15th Hussars, and 19th Hussars were in reserve in the G.H.Q. line. The night was less disturbed by gun-fire than usual, and even the rifle fire and itinerant sniping were of less volume than for weeks past. General de Lisle, noticing the strong westerly breeze die away, and the wind shift to the east during the course of the afternoon, sent a warning to the troops in the trenches to be on the look out for a German gas attack next morning. At earliest light on Whit Monday, the 24th of May, the Hun gas came. Before three o'clock in the morning, the yellow-green haze was drifting slowly on the light breezes that heralded the coming of the dawn. Over the eastern front of the Salient the smoke-cloud came from near Wieltje to the Zonnebeke road, and on to the south over the Menin Road. The 28th Division troops, from the Ypres-Roulers railway to the Bellewaarde Lake, were in the thick of it, and were driven back _en masse_. The trenches of the 18th Hussars and 9th Lancers were also in the path of the noxious fumes; but the 1st Cavalry Brigade troops further south escaped them. For an hour the gas rolled westward, accompanied by a cyclone of shell-fire, and followed by a determined infantry attack. No part of the cavalry line felt the gas more than the left of the 18th Hussars, which was held by a squadron under command of Captain MacLachlan, who arrived at Vlamertinghe from England at seven o'clock the night before. MacLachlan, with some of the half dozen other officers and 130 men sent out to replace the casualties suffered by the 18th Hussars on May 13th, was tramping through Ypres within half an hour after he joined the regiment. New to Flanders and the Ypres Salient, his experience of a gas attack before he had been in the firing line twelve hours was a trying one. MacLachlan was impressed by the warning to be on the watch for gas, and was in his forward trenches, awake and alert. His respirator was ready, and he repeatedly told his troopers to see that theirs were ready also.