Trench warfare dominated the fighting in WW1. After the initial hasty digging of trenches in the early days of the war, as each side dug in to defend their lines, trenches evolved to be more complex and sophisticated, including digging them in a stepped or zigzag shape.

Why were trenches dug in a zigzag pattern? Zigzagging trenches with sharp corners helped remedy several fatal flaws learned from early trench warfare:

One of the key advantages of a zigzag trench is its ability to contain blasts. In a straight trench, the blast from mortar or artillery fire would travel unimpeded to either side. However, a trench with frequent bends could confine explosions to smaller portions of the trench, reducing casualties.

2. Zigzags help slow an enemy down after capturing a trench

A straight trench meant that breaching a portion of it gave a long line of sight and the ability to fire down the trench which could aid attackers. Angles and corners from the zigzag or wavy shape of a trench meant that line of sight was reduced and gave better defensive positions with cover and concealment.

So, the simple change from a straight trench to a zigzag gave defenders significant advantages, and both sides used the design during the war. It's painful to imagine the tragic lessons that led to this evolution in design.

I learned about zigzag trench design from a children's book about WW1: 50 Things You Should Know About The First World War, by Jim Eldridge. It's striking how such a simple design change can have a significant effect. It's also a great example of how a simple solution can seem so obvious in retrospect and yet may take time to develop.

One of the trends of evolution identified in the theory of inventive problem solving that always fascinated me and has myriad applications is how straight lines in products typically evolve to jointed or bent, then wavy lines. As the theory would say, a straight line has unused potential, and someone will find an advantage in introducing a bend or bends. I sketched a similar trend about flat surfaces having unused potential.

The Imperial War Museum has a great 9-minute video explaining trench warfare, which discusses the zigzag or stepped design in this sketch.

Zigzag trenches

So the story goes, as told by Stephen Sigler, Nature May 1989:

"The US military studied fighter planes returning from missions to try to improve their survival rate and were considering adding heavy armour to those parts of the plane that tended to show the greatest concentration of hits from enemy fire, until statisticians pointed out the fallacy of that argument. The more vulnerable parts of the plane were those with the fewest hits; planes hit there tended not to return at all. The single most vulnerable part, the pilot’s head, was without serious scar in the sample of planes that returned."

It’s easy to draw correlations from what we see in front of us. But what we see usually represents just a small part of what has happened. Focusing on the evidence we can easily see at the expense of that we can’t leads to survivorship bias. To say it another way, when Bill Gates drops out of college and starts Microsoft it might seem like dropping out is a path to success for others too, but that ignores all the dropouts who didn’t create Microsofts and consequently you didn’t hear about.

Silent evidence — the evidence that we don’t or can’t easily choose to consider — is a term from Nicholas Nassim Talleb.

When trying to discover the veracity of the planes story I enjoyed Bill Casselman’s American Mathematical Society article on The Legend of Abraham Wald. The postscript points to some of the source behind the story including a mention of Stephen Sigler’s letter in Nature quoted above.

I covered survivorship bias before, but I like this story so much I thought it was worth doing again.

Survivorship bias

The Two Generals Problem is a fun thought experiment highlighting the challenges of communicating over an unreliable channel. Your message may or may not get through, and how will you know if it didn't?

The situation is that two armies on either side of a hostile valley are trying to coordinate an attack, and they want to attack simultaneously to be sure to succeed. The trouble is, to coordinate, they have to send brave messengers through the hostile valley to the other camp, and the messengers may or may not be captured along the way.

To coordinate the attack, you have to know that your message got through, which you’d know if you received a confirmation. But how would the general sending the confirmation know that their confirmation got through unless they received a confirmation of the confirmation? And on…

The two generals problem

The OODA loop is military strategist John Boyd’s framework for combat operations that also turns out to apply quite well to businesses and learning in general. It emphasizes a rapid cycle of Observing, Orienting, Deciding and Acting.

Though it’s not so different from the classic test-learn cycle or a good design process, Boyd’s framework has a lot of nuances. I found applying it to my own life valuable because:

The faster you can do this loop—in your work or in a conflict of any kind—the more solutions you can try and the quicker you will learn.

If you’re competing against others, completing your OODA loop fast and acting to change the environment for them means you can disrupt their loop and force them back to the observation step before they can act. It slows them down, creates confusion and gives you an advantage.

To apply the OODA loop to a business context, it can help to reconsider the points on the cycle as Frame, Strategize, Test, and Gather.

I learned about it from Reid Hoffman’s excellent Masters of Scale podcast.

The OODA loop features in my book Big Ideas Little Pictures

My original OODA loop sketch was an animation

War sketches