Less Is More — Or How To Replace A $25,000 Bomb Sight For 20 Cents

Depending on who you ask, the Norden bombsight was either the highest of high tech during World War II, or an overhyped failure that provided jobs and money for government contractors. Either way, it was super top secret in its day. It was also expensive. They cost about $25,000 each and the whole program came in at well over a billion dollars. The security was over the top. When not flying, the bombsight was removed from the plane and locked in a vault. There was a pyro device that would self-destruct the unit if it were in danger of being captured. So why did one of the most famous missions of World War II fly with the Norden replaced by 20 cents worth of machined metal? Good question.

You often hear the expression “less is more” and, in this case, it is an accurate idea. I frequently say, though, that “just enough is more.” In this case, though, less was actually just enough. There were three reasons that one famous mission in the Pacific theater didn’t fly the Norden. It all had to do with morale, technology, and secrecy.

The Mission

A B-25 in Flight

Sometimes, appearances matter. If you ever test a user’s reaction to waiting for output, you will find that they are more tolerant of watching a screen of data scroll by slowly than they are of waiting less time for the data to appear suddenly out of nowhere. Doolittle’s raid on Japan was like that. It wasn’t really practical and was unlikely to change the outcome of the war, but it made people feel like something was being done.

After the attack on Pearl Harbor, the United States was seriously upset. Even though Hawaii wasn’t part of the mainland, it was part of the country and Americans keenly felt the threat that Japan could strike American soil. America needed to strike back but had few options. Much of the navy was out of commission because of the attack. The planes of the era couldn’t cross the Pacific loaded with bombs and fuel. The Americans had no missiles that could make the trip, either.

Enter Jimmy Doolittle. Where nearly everyone else thought there was no way to retaliate, Doolittle and a few others were convinced he could find a way. He formed a squadron of B-25 Mitchell Bombers and set out to prepare them for the trip to Japan.

Less… Much Less

The B-25 had a normal range of 1,300 miles, but it needed to go at least 2,400 from an aircraft carrier to hit Japan. Everything had to go to lighten the planes and make room for additional fuel tanks.  Guns, blast plates, cold-weather equipment, and some radios had to go.

A Norden ready to fly

New fuel tanks took up some of the space created. One other thing that had to go was the Norden bombsight. It wasn’t good for low altitude bombing was the official story. However, the weight was also significant and — perhaps the main reason — it seemed possible that at least one of the planes might be shot down and captured. The Army Air Corps did not want to risk the Norden. Turns out, the Germans got the plans delivered to them before the war and had their own version of it, but no one knew that at the time.

But You Still Need a Sight

Photo by [Pi3.124] CC BY-SA 4.0
However, you still need some kind of bombsight. That’s where Charles Ross Greening with some machining help created what he called the “Mark Twain” bombsight. The newspapers would later call it the “twenty-cent bombsight” because of the few materials it used. Here’s a description from Wikipedia:

[The Mark Twain] consisted of a quadrangle measuring 7 inches (18 cm) by 7 inches (18 cm), inscribed with a 90° arc in 10° increments, and placed horizontally on the Norden mount. When the quadrangle was turned left or right, a handle deflected the Pilot direction indicator, indicating the prescribed heading for the pilot. A vertical piece, measuring 5.25 inches (13.3 cm) by 7.25 inches (18.4 cm), set the dropping angle, based on bomb size, altitude, wind conditions, and ground speed. The vertical piece had a sighting bar with a “V” notch at the rear, which was to be aligned with a point at the front, just as in a rifle sight. The bombardier aimed the bombsight in the direction of the target, raising the tail as he got closer, until he reached the dropping angle, when he would release the bombs.

Simplicity, itself. Yet less is more. It is possible that the cheap sight may have worked better than the Norden’s actual performance, at least in some cases. The raid was sort of a success. It didn’t manage to do much real damage and all the planes were ditched, but it had a positive effect on Allied morale and the opposite effect on the Japanese population.

Lessons Learned

There’s a famous old story that NASA spent money to build the space pen and the Russians simply used pencils. Turns out that the story isn’t true (NASA didn’t pay to develop the Fisher space pen). But it reminds me of the 20 cent bombsight. While you can cut too far, sometimes less really is more.

I think we forget this too often. We often hear of relatively simple systems failing due to having too much software layered on top of them unnecessarily. For example, check out EDN’s report on the infamous Toyota firmware problems. Granted, this could be a case of poor workmanship more than over-complication, but then again, I’d rather have a handful of dedicated CPUs doing very specific tasks on bare metal than some big processor with an RTOS handling so many life-critical tasks.

If you want to know more about the hype around the Norden, we talked about it before. We’ve also talked about the era’s heavy bombers, too.

Headline photo: Norden Bombsight at Computer History Museum by Allan J. Cronin, CC BY-SA 3.0

63 thoughts on “Less Is More — Or How To Replace A $25,000 Bomb Sight For 20 Cents

  1. “I’d rather have a handful of dedicated CPUs doing very specific tasks on bare metal than some big processor with an RTOS handling so many life-critical tasks.”

    Amen brother! Systems built according to that philosophy have more resilience, as well as generally being easier to troubleshoot and repair. Also, that kind of modularity can allow for more and easier reuse of already-proven designs.

    1. Easier to troubleshoot and repair?

      Wouldn’t it be easier to just conclude that the single CPU is broken and replace it – rather than hack around finding which one of the particular chips is misbehaving, how, why, and which of the many parts you need to replace.

      The problem is that expert diagnostics costs $60 an hour and if the problem is non-trivial, two or more working days. That means anything under $1,000 is cheaper to just replace.

      1. Yeah, I’d rather enforce best-use for an RTOS than manage communication protocols between myriad MCUs.

        Of course, there’s situations in which proliferated CPUs make a ton of sense, but breaking up individual tasks for a piece of tightly-tied functionality is not something I’d do it for.

        1. I’m guessing you’ve never designed anything actually safety-critical. Small systems with a small number of responsibilities each are much easier to audit than large, monolithic systems with RTOS complications. Communication protocols can be very simple (like CAN bus used in automotive and aerospace). Also, splitting tasks properly can lead to inherent fault isolation, and non safety-critical tasks should be isolated from safety-critical tasks anyway.

          Even if you’d “enforce best-use for an RTOS”, you’d have to completely audit the RTOS code, which, for a real OS, is extremely complicated and expensive.

        2. Then you would be absolutely shocked if you knew how many MCUs there are on an aircraft.

          With avionics safety it’s not just about the boundaries of processes, u-processors or functions. It’s about the domains of authority and the humans who exercise those domains of authority and the associated responsibility. We have terms like defined state, failure mode, intrinsically safe, authorised, certified, conditionally serviceable.

          The problem with the car industry is that all these things are in-house and easily corruptible.

          Many different manufacturers make much of the avionics on an aircraft and there is rarely ever even a slight issue with something made externally from the aircraft manufacturer.

          Some car controller code looks like a spaghetti bowl of random libraries much like you would expect from a school student coding with an Arduino.

          Car safety should be looking at linking multiple defined state machines. This would create different domains of responsibility and I am sure the result would be safer vehicles.

          I’ve had a CEO of an internation airline company breathing on the back of my neck when I am conducting urgent repairs to critical ground side equipment an an international airport, that is holding 10 or so aircraft on the ground at a cost of about $15000 per minute per aircraft.

          He was pressuring me and asked how long it was going to take and I just said “twice as long with you here” so he left.

          So when a shitty little avionics engineer can tell a CEO go #%^%$ over concerns of safety issues then corruption doesn’t happen easily.

      2. A good troubleshooter doesn’t need to “hack around”. If the trouble is well defined, and different circuits control different things, it is much easier to isolate the problem.

        If your taillights go out, do you “hack around” your car, checking the brakefluid, the wiper fluid levels, the radio? Or do you go right to checking systems that control the taillights?

        If you have a car without everything controlled by a single brainbox, there is just one circuit to troubleshoot. If everything is controlled by one centralized CPU, not only can’t you easily troubleshoot it, it is =very= expensive to replace.

        1. On the golf mkV the air conditioning compressor can stop working due to low vacuum in the brake booster.
          If the ecu detects low brake vacuum it sheds power draining elements to enable the throttle to close as much as possible in an attempt to increase manifold vacuum

      3. If Right To Repair is important to owners of John Deere tractors, surely tha same could be said of basic automotive repair. Oil, spark plugs, etc.
        If my brakes started misbehaving, the ability to swap out sensors and a mini brain module bypasses the need for that $60 per hour expert.

        You could also have a side business repairing the dedicated CPU modules, but that’s another story.

    2. Yep, I would argue that as a matter of principle, when designing safety-critical equipment you should assume “An OS will always fail”. Doesn’t mean that you can never use an OS, but it means that any safety interlocks must be implemented outside the OS

  2. This is mentioned in “Thirty Seconds over Tokyo”.

    Well, not the bit about the replacement. I assumed they didn’t want the bombsite captured. Besides, the whole thing wasn’t about a surgical strike, but to just do something at the Japanese.

    That they used a 20cent replacement in itself means nothing.

    1. “Thirty Seconds over Tokyo, or how I joined the Mile High Club”.

      Well the Doolittle raid wasn’t meant to hurt the Japanese or even for revenge against the Japanese (time for that would come) but to lift U.S. civilian morale. The Pearl Harbour attack was quite a shock to America and there was some concern that they couldn’t do anything against Japan (and consider what was happening in the Philippines) bad news all around, the Doolittle raid was a great morale boost for America exactly when they needed it and that is what it important about it.

      1. Boost US/Allied morale and damage Japanese morale; I’ve read that the idea that the Emperor himself might be in danger from US bombing caused some real changes in the movements of the Imperial Navy, which was pretty much steamrollering everyone in the Pacific Theater at the time.

        (Though possibly the most significant outcome from the Doolittle raid was the set of Japanese reprisals against the Chinese civilians in the coastal provinces where the aviators landed; an estimated 250,000 were killed, and some 20,000 square miles of populated land was razed.)

    1. Came here to say this too – plus I think they used a pair of spotlights in the wings to measure ground height at very low altitude – when the two beams became a dot, you were at the correct height.

  3. The B-25 pictured in flight is the “yankee warrior” of the Yankee Air Museum in Belleville / Ypsilanti Michigan. She was repainted a couple years ago as “Rosie’s Reply” and tours the country on the airshow circuit. She is a combat veteran B-25, having flown missions in the italian and North African campaigns.

    Uniquely, she is the only airworthy B-25C model. On paper she is classified as a B-25D, however the FAA only certifies D and J model B-25’s. C and D models are essentially identical, but the letter indicates factory of origin. C’s were built in Compton California, while D’s were built in Kansas City. (Or vice versa, I’m going from memory.)

    1. Huh Ypsilanti! I used to live there. Not far from the world’s most phallic tower. Odd that I never knew of this museum, I’ll have to see if I can find it when I visit my brother.

  4. so the thing about pen vs pencil.. NASA Decided that having potentially Conductive Graphite Dust floating around in a oxygen rich environment was not necessarily the best idea..

      1. Same as Tang, created in 1957 and on the market in 1959. But often seen as invented for the space program because NASA used it early on.

        I read somewhere that it helped to cover the taste of water in the space capsule.

        1. Velcro – patented it in 1955.

          Many of the “spinoffs” from NASA are simply retcons to keep up the myth that NASA was instrumental or involved in creating them, whereas the reality is that NASA merely bought stuff of the market and put their logo on it.

          Otherwise they couldn’t have done the moonshot in time. The myth that it was so useful in terms of spin-off technology was made up after the fact when people started asking why it had to be done and why should we continue funding it.

      2. … and the part about the Soviet space program using pencils isn’t true as well, for the same obvious reasons (graphite splinters are not only bad for electronics but also can get into your eyes..very irritating). In the end the Soviets ordered a batch of Fisher space pens.

      1. The Soviets had lost cosmonaut Valentin Bondarenko in a fire in an oxygen-rich training environment, which seems to have been the final impetus to stick to a relatively Earth-like atmosphere mixture in all their spacecraft, from then until today.

  5. someone must have been reading my comments and posted an article to shut me up. lol. as long as the function is met, anything extra is frivolous and prone to breakage or malfunction.

  6. Another “less is more” example: WW2 created the need to rapidly train pilots. The planes of the time were so noisy that it was hard for an instructor and student to hear each other. The US government called for bids on an intercom system so they could communicate. Heath Company was by far the low bidder; so low that it was rejected outright. It was deemed impossible to provide the needed microphones, headphones, and amplifiers to do the job. But Heath insisted it be taken seriously, and even had to call their congressman to intervene on their behalf.

    So Heath’s “Airphone” was tested along with the others… and turned out to work the best, and so won the contract! It had no electronics at all — it simply used rubber hoses to connect the headphone earpieces to the mouthpieces.

    1. Do you have a source or a link to more information? I’ve never heard of these before and it sound like an interesting story. I’d love to see what these “Airphones” looked like, but unfortunately I can’t find anything searching for that. (No Google, I don’t want to search for earphones instead…)

      1. I’ve never seen anything like that, but the Heath company did start by making airplanes, and after Heath died in a flight, the company was sold and refocused on airplane accessories.

  7. I found the description of the bomb site to be incredibly wordy (and inaccurate, it’s not a quadrangle). Upon viewing pictures of it, I said “That’s just a protractor”.

    I bet the guy made his own because the Machinist told him that he couldn’t take his Starrett protractor and steel rule!

  8. So this is really just a “you could do it with a 555” story.

    The first prototype was in 1924. Aviation was still relatively new, and aerial warfare had had only one war. I thought they basically dropped traditional bombs off the side of the plane then.

    So they knew the need, but development started before much practical experience. They probably spent money because it was a new field.

  9. My dad along with Vernon Warren and “Bird Turd” Thomas were the top of their class so were selected to go to Norden Bombsight school either in San Antonio or The Spartan School of Aeronautics in Tulsa Oklahoma. After some months or longer they went overseas to the Pacific Theater. Dad never got to work on one as they were too secret even though he spent a lot of time learning how to fix them.

  10. I was a nurse for a good while and one of my patients trained for the Doolittle raid at the age of 14. Actually, it was a short take off contest among B-25 crews. He didn’t make the cut but I wonder how young (and skinny) some of those guys were.

  11. Punching my non-technical pet peeve button was the line “Even though Hawaii wasn’t part of the mainland, it was part of the country…” Attempting to read between the lines, I wondered why “not-the-mainland” would matter. Why do *I* care? Ten years after I moved from Hawaii to the mainland, it’s still nails on a chalkboard when someone refers to a trip from HI to the CONUS as “going stateside”, the Stars & Stripes flying over the terminal of any airport on the islands apparently not cluing everyone in.

    1. I don’t think there are lines to read between here. We did respond fully to the attack. But as a matter of physical security, if country X can strike New Jersey, that isn’t as frightening to someone in San Francisco. But they are still pretty angry about it. Same here. I never heard a word that anyone at the time or since suggesting that it wasn’t like they hit the US. However, it remains true they badly wanted to hit the west coast of the mainland but never had much success other than a few stunts with subs and balloons that were totally downplayed in the press. There was minimal damage to an oil field, a few forest fires and a baseball field damaged.

  12. “When not flying, the bombsight was removed from the plane and locked in a vault. There was a pyro device that would self-destruct the unit if it were in danger of being captured.”

    The Germans had a complete set of plans for the Norden bombsight courtesy of the efforts of an employee named Hermann Lang, a naturalized German immigrant who worked for Norden in the Manhattan plant and smuggled out the plans in 1940, which went to Germany. The German Lofte 7 bombsight was developed by people who had access to the data from Norden and while not a copy of the Norden design its likely they
    learned a lot from it.

  13. 1. The Doolittle raid actually accomplished several militarily important things. It misled the Japanese about the true range of US bombers and it caused Japan to expend resources and reserve fighter aircraft for homeland defense efforts that could otherwise have been used in other places.

    2. Saying the bombsight could be replaced with a simple iron sight is a vast oversimplification. Yes, an iron sight could be used if you are low enough and you do not need to be accurate compensating for speed and wind. The Norden bombsight was special because it computed lead and was integrated into the autopilot system allowing the bombardier to control the aircraft on the bomb run. It circular error probable was 75 feet which would be very hard to achieve with iron sights.

    1. I read the wikipedia entry about the Norden. One thing I’d never thought of was if the plane isn’t level, the trajectory is different. So “bombsight” is kind of misleading, since it factors in a number of variables. You aren’t looking down and firing over the target, it’s calculating so the bomb is dropped so when it arrives it will hit the target.

      1. Of course. Not a bombsight, but a fire control computer. These were big on naval vessels for firing their big guns, but they were big, heavy analog computers. I’m guessing that the chief innovation of the Norden was making it small enough for use in aircraft.

  14. It’s worth mentioning that an accurate bomb sight is critical to take out important targets with minimal civilian damage, and the Norden bombsight was used to great effect in Europe. Leaders in the pacific theater used carpet bombing instead, so the bomb sights didn’t need much accuracy. Their carpet bombing campaigns were so prolific that they created more deaths than nuclear bombing campaigns.

  15. My wife’s grandfather was an engineer working in bearings, and a long-standing family story was that he’d invented some new kind of bearing that was absolutely crucial to the Norden sight; it kind of grew over the years, until everyone was convinced that his contribution was _the_ thing that made the sight possible at all. Of course, none of the books and articles out there mention him at all; my wife’s concluded that there was a bit of self-aggrandizement going on.

  16. Regarding the security surrounding the Norden sight… During World War II my father worked for Sperry. One day, my mother returned home and heard from the neighbors that in my parents absence they had taken delivery of a postal package: a good sized tube with Top Secret stamped all over it. They were concerned and curious. My mother made up the story that it was actually advertising material shipped at a lower rate if marked as classified. My father opened the tube and inside he found an entire set of blueprints for the Norden sight!

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