Hiding in plain sight. You might say that this saying has two meanings. The first means to deliberately concealing something and yet it remains visible. For example, imagine somebody in disguise: you see a person, but you don’t see his real identity.

During the Second World War, the Pacific island of Guam was occupied by Japanese forces. As American forces prepared to expel them in July 1944, a U.S. Navy destroyer was ordered to fire upon an unusual target: some Japanese latrines. Not the most illustrious target the gun crew was hoping for — shoot up some latrines? — but the firing plan left no other targets available. Aye, aye, sir!

Boom!

KAH-BOOOOOOOOOOOOOOOOOOM!!!!!!!

The explosion was immense.

What the heck happened? The gun crew got worried. Did we just use our most powerful high-explosive shell to blow up a bunch of latrines? We were supposed to save that one!

No, they hadn’t used a super-shell. The Japanese had filled the latrines with spare ammunition. The Japanese assumed the Americans would not waste naval gunfire to shoot up a bunch of latrines. (Did that assumption make the Americans smart? Or stupid?)

That version of hiding in plain sight involved the deliberate. (After all, the latrines were not camouflaged.) But what if the hiding isn’t deliberate? Or, as Sherlock Holmes might say, “You see but you do not observe.” For example, when was the last time you saw a fire extinguisher? The occasion was probably more recently than you realize, because fire extinguishers are stored in corridors, in stairways, perhaps even in your office. You know its importance but you take it for granted. Until you need it, you don’t notice it.

During the Second World War, the Pacific island of Tarawa was occupied by Japanese forces. As American forces prepared to expel them in November 1943, American reconnaissance planes photographed the island. The images were so crisp that American photo interpreters were able to identify even the Japanese latrines. (This was before the battle for Guam, so nobody imagined they were anything but latrines.) The Japanese had not camouflaged them and presumably didn’t think to. After all, what of military significance can you learn from a latrine?

Quite a bit actually, even without entering it. The Japanese installed only as many latrines as they needed — so precisely, in fact, that each latrine served a standard number of Japanese soldiers, i.e., a standard ratio. American intelligence analysts counted all the latrines, multiplied that sum by the standard ratio, and — voilà! — got an estimate of how many Japanese soldiers were on Tarawa. After the battle, captured Japanese documents revealed that the American estimate was remarkably accurate.

I must confess to some doubts when I first heard this story, for it sounds so bizarre. After doing some research into this story, however, I am convinced that it is essentially true. Hiding in plain sight. The Japanese could see their own latrines but they hadn’t observed what this meant: each latrine was more than a military out-house, it was a clue for the enemy.

What those Japanese soldiers on Tarawa did wrong was, in military terminology, a violation of Operations Security or OPSEC. Clues left in plain sight, for the culprits failed to realize those were clues.

You don’t have to be in the military to realize this story offers a lesson, a warning, for all of us today, including for you personally. For as we live our lives, we leave traces of ourselves in cyberspace, in social media, in our blog postings and comments, in the memes we “like” and store, in our financial transactions, and physically in our neighborhoods, our workplaces, our favorite hang-outs, even in the very public places we frequent — city streets, parks, subways, buses, taxis, trains, airliners — as we use our cellphones to talk and text with the self-assumption that nobody nefarious is noticing those traces of ourselves and collecting those clues. Outwardly, we complain about identity theft, about “Big Brother” and about our privacy being at risk — but while we see the news headlines about such dangers and violations, too few of us observe what traces of ourselves we are leaving in plain sight.

The lesson and warning is that we don’t always notice what potential clues we are leaving around about ourselves and our behavior. But we should.

— John G. Heidenrich