British Tank Development.

I am not sure you can fully separate durability and reliability, an engine is only durable if it can reliably achieve a stated lifespan.

If 9 in 10 tanks achieves the predicted lifespan of 1000 miles that would be considered reliable and anything after that could be considered durability. Even if a tank is specified to last 3000 miles and 9 in 10 tanks reach 2500 miles then that is still a reliable engine but lacks the durability to actually achieve what it should. It is all well and good knowing that X tank could drive for 3000 miles if well maintained and treated just right but if only 1 in 10 manages then it isn't reliable or durable.

Knowing the tanks will all need servicing after 2500 miles even if they are quoted to last 3000 miles is still a great aid to the logistics network to plan around than if 9 of 10 tanks drop out at random intervals across the route of march. Not that what you said is wrong but the durability vs reliability isn't quite as distinct as you said.

 

They appear to be quite distinct to me:

Durability = the vehicle and its components last X miles between major overhauls, if maintained according to the schedule
Reliability = the vehicle and its component don't break down, if maintained according to the schedule

As a break-down may not be related to durability as defined above, it is a different matter.

All the best

Andreas

 

That is what I was trying to get at but I chose my words poorly, I just meant to say you can design a durable engine but that doesn't necessarily make it reliable.

 

Ah yes, that is certainly true.

All the best

Andreas

 

The point is though that the low-durability early war tanks in places like the desert and USSR were inevitably run past their life mileage, therefore guaranteeing unreliablility. That is why in practice more durable tanks were, from the point of view of the end users, more reliable.

 

Is it appropriate to think of reliability of components versus the durability of the system? My brain's struggling to get the fag paper between them at the moment.

Fighting, Support and Transport Vehicles, and the War Office Organization for Their Provision: Part I: Common Problems hasn't offered any insight yet...

 

It's easier to think in terms of mileage. Durability = more mileage before you either scrap or overhaul, or try to keep the damn thing running despite it being knackered.

 

The way I see it.

Durability - the ability of the component (and the sum of components, such as the vehicle) to reach the design age/milage, provided all the required maintenance was undertaken. Think about pistons wearing out, or engine blocks cracking. Basically, if an item is lifetime limited, then you expect it to reach its design life, provided you looked after it.

Reliability - the ability of a component (and the sum of the components, such as the vehicle) to reach the expected mileage between service intervals without breaking down/requiring additional service. This is a different standard from lifetime. The failure in this case is not necessarily a complete failure, it could be e.g. an engine overheating due to a water leak because a washer wasn't replaced in time and failed. This would mean the engine can be restarted once the radiator was refilled, so it is still 'durable', and it was reliable, even though it failed, because this was operator maintenance, not design error. But assume that the washer was a faulty design, and instead of lasting 500 miles it only lasted 125 miles. Now your engine has become less reliable, because even if you change the washer on the prescribed 'every 500 mile' schedule, your engine will still overheat.

All the best

Andreas

 

Another way to look at durability is this:

Operation Barbarossa - the Germans can push on past the Dnieper if they want to because their tanks aren't worn out.
Operation Compass - Dicky Creagh can push on to Tripoli if he wants to because his tanks aren't worn out.

Dicky's tanks might not be perfectly reliable, and may require a quick repair job every six hours or so, but they can still cover the operational distance required and achieve a far more resounding and historically decisive victory. Basically, unreliability is an inconvenience, while lack of durability is an operation stopper.