On Tigers and Coronaviruses

Some of the most important engineering lessons were demonstrated on the tank battlefields of World War II when German Tigers faced off against Soviet T-34s. The Tiger tank was a technical masterpiece of for its time with many features that did not appear in allied tanks until after the war. Despite its much heavier armor it was able to match the speed of lighter enemy tanks and keep up with its own light tank scouts. The armor featured almost artisanally welded interlocking plates. The ammunition featured innovative eletric trigger primers and high penetration tungsten shells. The double differential steering system allowed the Tiger to rotate in place. A complex system of interleaving wheels distributed weight evenly, improved offroad mobility and even allowed mobility with damaged tracks. But while the Tiger was a star on the blueprints, it was a disaster on the Eastern front, not because of its combat performance but because it was a logistical and operational nightmare. The heavy armor made the tank a gas guzzler, which made tanks inoperable when supplies were low. The electric trigger primers would fail in cold weather. When rotating in place the gearbox would often break and German training manuals forbid the maneuver. The highly specialized internal mechanics made production slow and meant the tank often could not be repaired in the field but had to be sent back to Germany, and the great logistic costs meant that Tigers couldn’t drive to the front but had to be brought there by rail.

The Russian attitude toward the T-34, on the other hand, was that making a tank a work of art was a waste of time if its purpose was move a gun into position just before being destroyed. Systems were designed as simple as possible to improve mass production speed. Armor was often welded with gaps between plates that you could stick your fingers into. To prove the tank’s mobility, the T-34’s designer Mikhail Koshkin drove the tank through snowstorms from Kharkov to Moscow and back. The tank lasted the journey, but he died from pneumonia contracted during the trip. When German armor outclassed the tank’s 76 mm gun, instead of designing unique solutions the Russian simply stuck an 85mm anti-aircraft gun into the turret. The Germans built 1347 Tigers; the Russians built 84,070 T-34s.

The Soviet success provides many valuable lessons for those trying to design and implement solutions for the current coronavirus outbreak. It is critical to understand the problem that you’re trying to solve, the resources that you have available, and how those resources can be applied most directly towards solving that problem. Unnecessary complexity leads to increased failure and causes problems in operation through low reliability and throughout the supply chain by creating material bottlenecks. Production capacity is necessary for overpowering the problem and simple minimum-viable-product design improves total system throughput and allows for mobilization of non-technical personnel. Materiel, personnel and time are all limited resources that cannot be used on discreationary objectives. But most importantly, it is necessary to be radically honest because you need to design for the problem that you have, not the problem that you want.

Already we’re seeing these principles being violated in the US response to the growing COVID-19 pandemic. Time and initiative are some of the most limited resources available in critical situations like this. Napoleon said ‘space we can recover, lost time never’. Despite this, leadership has been absentminded at all levels of governance, from the local to the federal, even to the global. Most officials appear to be stuck in a daze unable to take action until natural events force their hand. The comparison to Stalin hiding in shame from the public during the first days of the German invasion is impossible to resist. Even on March 9th the WHO is still making absurd statements that the threat of a pandemic “has become very real“, a phrase that can only still make sense to a bureaucrat waiting for a case in the notorious Madagascar before declaring that the pandemic is in fact not in our imaginations. In the meantime the CDC has demonstrated inability to provide testing kits at the required capacity, furnishing only 2000 testing kits in the same time that South Korea mobilized over 100,000 tests. In fact, the CDC made matters worse by preventing hospitals from developing their own tests and requiring them to route all testing through the CDC, creating a capacity bottleneck, increasing system complexity, and adding the travel time as an additional lead time between testing and results. Furthermore, the CDC increased complexity of their tests by using three primers, causing the initial batch of the kits to fail validation because of varying performance between the primers. In the meantime, the President’s bizarre and false ‘everybody who needs a test gets one’ cheer campaign is deafening.

With nearly two months of time since the initial Wuhan outbreak wasted, the US is finally scrambling to develop a strategy that it can communicate to the public. Much of this scramble involves an academic debate over how deadly or how infectious this virus is, as if the pundits are trying to find some economic optimization point at which simply doing nothing would be justified. Lost in the debate is the fact that this point does not exist because we know from in vivo experience in China and Italy that this coronavirus is both highly infectious and highly deadly, far above the rates of the flu that it still keeps being compared to. The frailty of the modeling exercise is that it depends on information to model off, which we know is dramatically incomplete due to the testing bottleneck, a conclusion that is validated by the constant stream of surprise cases that are now cropping up across the country.

The engineer’s task of developing a solution to the problem begins with understanding the nature of that problem. First, accept that this is highly infectious and highly deadly virus and that the hyperparameter tuning of the modelers is effectively irrelevant at this point. Two Italian physician posted extensive descriptions of the situation in the northern Italian lockdown. Their reflections are mandatory reading and corroborate what we know about what happened in Wuhan weeks earlier. Now that transmission is indigenous to the US, proper risk management requires us to assume that without intervention the same will happen within the next few weeks. The exact CFR of COVID-19 will be irrelevant to the overflowing emergency rooms, the shortages of respiratory ventilators, and the insufficient clinician staff. The second thing to understand is that right now there is no vaccine or cure against the infection. Normally the healthcare system provides curative interventions that directly treat the infection, but in this case the only known countermeasure is our own immune systems, which means that the only thing the healthcare system can do is provide stabilizing interventions to critical cases until the immune system can do its job. Finally, it’s necessary to understand the unusual virulence of this infection, which devastates the elderly and chronically ill while leaving the youth relatively unaffeted.

Combining these parameters, we are able to make a clearer formulation of the problem. The primary mission before the nation is to save as many elderly and chronically ill as possible by preventing the healthcare system’s resources from being overwhelmed. When accounting for the ease with which this infection spreads, the recorded autochthonous cases and the timeline over which the infection has shown to operate, it can be assumed that containment is impractical, if not impossible, at this stage. We are already within the critical window. In the words of Martin Sheen’s Robert E. Lee, “there is no time for that“. The primary objective therefore becomes not limiting the total number of cases, but limiting the rate at which new patients enter the healthcare system, and most importantly the ICUs, such that this rate does not exceed the rate at which people recover and leave the system. If the intake rate outstrips the exit rate system performance begins to quickly degrade as patients are unable to enter the required facilities, materiel shortages prevent delivery of appropriate treatment, and exhausted clinical staff begin to make errors that put patients and themselves in danger. The healthcare system cannot increase the rate at which patients immune systems will function and it has limited ability to effect the intake rate. It can and should redirect resources from discretionary procedures towards COVID-19 treatment, but this only increases the treatment-in-progress capacity and has no effect on the intake rates. Furthermore, the capacity of the most important resources like ICU beds is highly inflexible because these are more complicated systems than simply shoving more stretchers into a space. Recovery for critical COVID-19 cases has been shown to be 3-6 weeks and 2 weeks for even mild cases.  This is much longer than the average 3.3 day ICU (+5 day non-ICU recovery) or 4.5 day regular hospital length of stay. From Little’s Law we know that the patient load is proportional to the intake rate and recovery time, which means that an increase in the overall ICU intake rate by only 25% would double ICU utilization. It’s easy to see how the system capacity quickly becomes exhausted. This will be especially devastating for highly optimized systems like the NHS where the ICUs operate at 90% utilization and only a 2% increase over the base intake rate will result in all current capacity being exhausted.

Without the ability to affect rates directly, this means that the control intervention has to extend beyond the healthcare system and be applied at the level of the entire national community. It must be again emphasized that at this point there is insufficient information to determine the spread of this disease and there is still insufficient testing capacity to improve this information. There is therefore a high non-zero probability that the US is ALREADY past the point where intake rates would outstrip current healthcare capacity. Furthermore, delaying significant action increases this probability with every day. Because of the speed with which this infection progresses it is therefore necessary to implement dramatic interventions to minimize further spread until testing capacity can catch up and information on the morbidity is more complete. In short, total mobilization of the society is necessary. Half-hearted measures such as recommendations to stay out of public spaces or to wash your hands are not sufficient. These solutions are in fact highly complex because it requires the cooperation of millions of independent actors. Such complexity only creates risk of failure in a time when insufficient information requires a restriction on the degrees of freedom to the problem. The only way to ensure the risk of further spread is minimized is by halting all public events, travel, commercial activity etc. Right now it is necessary to buy our clinicians as much time as possible. Mass quarantine is a simplistic, dumb, even brutal, tactic but it fits the requirements of the problem and desired outcome. These restrictions can be lifted as the healthcare system’s utilization by COVID-19 is validated as sustainable and testing capacity improves our information and enables effective containment and quarantine, but delaying them until the last moment implies a vulgar acceptance of risk to American lives for the sake of preserving economic activity.

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