German WW1 flamethrower - Western Front, 1917 Compare the dimensions. (Bundesarchiv Bild 183-R22888)
JR - I’m going by memory here, so please forgive the inevitable errors and vagueness. I believe the Germans were the first to use the flamethrower in WWI, and it was while on the offensive. IIRC, they place either had trenches that were relatively close together, or tunnels were used to get the weapons in range (maybe 50 yrds?). These were big things, not manpacks, and might even be the type of weapon shown here. The use of the weapon was terrible in it surprise and terror value.