The Russian revolution of 1917 resulted in a peace treaty between Russia and Germany and the closing of the Eastern Front. Thousands of troops and equipment were transferred to the Western Front and on 21 March 1918 the German “Spring Offensive” commenced. They advanced 40 miles over the next 6 days - England and its allies were facing defeat.
With the whole Allied line on the Western Front in danger of collapsing troops were rushed into the threatened areas, including the New Zealand Division.
This return to the Somme region over cost some 2400 casualties, including more than 500 dead over 10-days of effort. The Germans, whose depleted and over-extended units were unable to hold onto their gains during the Allied counter-attacks that began in July.
For more information:
Spring Offensive, New Zealand and the Second Battle of the Somme / Glyn Harper 2003
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