I don't know what this adds (maybe just clutter) but this Darwin article written around the time of WWI talks of trenches, bunkers, TOC, the natural, and MacKenzie.
"Dr. Mackenzie is a well-known golfing architect in the North of England and incidently gained the prize for the best design of a two-shot hole which was recently conducted by Country Life newspaper and for which Mr. C. B. Macdonald gave the prize. The hole which he designed or something like it may some day be tackled by the golfers on the new course at Long Beach, L.I.
Dr. Mackenzie, moreover, served in the South African War so that he has a practical knowledge of trenches as well as bunkers. His lecture was founded on the assumption that an invasion of England was quite within the limits of possibilities; that in such an event civilians could make themselves very useful in digging trenches: that foremen would be needed who understood how to do it and who could be better men for the job than greenkeepers!
It would take far too much space to expound all or anything like all his interesting views. Very shortly his point was that the modern trench is not half so invisible as it ought to be. Either, it is in the form of an old-fashioned bunker with an abrupt rampart or turf wall in front of it which is the most clearly visible thing in all the world or it is merely a hole dug in the ground and is like the ordinary pot bunker.
The type of entrenchment which Dr. Mackenzie prefers corresponds rather to the bunkers at the twelfth hole at St. Andrews. I suppose a good many of your readers have stood on that twelfth tee and seen an apparently open and innocent plain of grass stretching away before them: likewise, have they hit what they deemed beautiful tee-shots and found them trapped by bunkers that are lurking everywhere unseen. Strangers to the course complain bitterly and not perhaps without some show of reason. The secret lies in the gently sloping bank of the bunker, which is of the same color of the surrounding country and appears to be no more than a natural undulation.
When the bunker is artificial it is well made by slightly exaggerating a natural rise in the ground so that its contours harmonize with the undulations of the surrounding country. There is little doubt that this is a very good kind of bunker: it looks the neatest, nicest and most natural and can be made so as to be invisible from the tee, where the player considers he has a right to see it, and from nowhere else.
Dr. Mackenzie gives very good reasons for thinking it the best kind of entrenchment and also excellent and detailed advice for the making of loop holes, the drainage of the trench, protection from shrapnel fire by means of an overhanging lip and much else of interest. What he has to say is extremely interesting, though we may hope that as far as the greenkeepers of Britain are concerned it may be of no more than academic interest.