The last phase of the Somme battle in 1916, Ancre, had hurt Shetland, through the loss of much of its Territorial Army commitment. The Arras offensive had caused more deaths, but the dispersal of Shetland recruits made the casualties take a different pattern. This continued in the Third Battle of Ypres, more often known as Passchendaele.

Between 7 and 17 June 1917, British forces successfully took Messines Ridge, Flanders, aided by an ingenious mining operation. On 31 July they launched another operation in Flanders. It was to end on 6 November, after it turned into a series of battles

General Haig had long wanted an offensive in Flanders. An attack there could neutralise the German submarine bases in Belgium. In April 852,000 tons of allied and neutral shipping had been lost. In local terms Shetland’s own losses in the Merchant Navy had continued to mount. Finally, it would relieve pressure on the Russians.

It was an attack across a flat plain. Heavy rainfall turned it into a bog. The battle became, along with the Somme, part of the enduring imagery of the war. A sodden stalemate of slaughter. The remains of Passchendaele village were taken on 6 November, gaining the allies five miles, and losing them 325,000 casualties.

The Germans had continued to refine their "elastic defence" concept. In response the British had deployed "bite and hold" tactics. Small advances well defended by artillery blunted counter-attacks. The Germans lost 217,000 casualties at least, which they could ill afford in the attrition warfare prevailing.

But there was no breakthrough, no advance to the coast. The submarine bases remained as they were.

More info: 

The Grieving Parents Kollwitz Wikimedia
Käthe Kollwitz: The Grieving Parents, Wikimedia image by Liège.