"More died from Flu in WW1 trenches than from bullets" - the purpose of trenches was to protect soldiers from bullets so very few should have died from that cause. WW1 is plagued with myths - www.bbc.co.uk/news/magazine-25776836
Honest John's Motoring Agony Column 20-10-2018 Part 1 - Wados
That's too literal a reading of the statement. "trenches" means battlefields, and is a figure of speech - metonymy. "The WW1 trenches" has been the common phrase to refer to the First World War for the best part of a century.