Thanks Chris (never heard of the Killefer plough before) - looks like those are massive mouldboards set up for a sort of chisel effect (sods turned either side). I guess "shallow" is relative, looks like it is meant to go far deeper than any simple mouldboard plough. Would take a lot of grunt to shift that plough at full penetration (3 feet maybe?). I wonder if the share-mouldboard assembly is hinged so as to skip over major underground obstacles? Can't quite make it out but should imagine some sort of provision would need to be made.
A 1937 version used in tree planting found via google, another version ( no pic ) was used after D-Day by the Royal Engineers for similar purposes as WW1 type. http://classes.forestry.oregonstate.edu/for442/gallery?page=2
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