Class failures

There is much that present day engineers, and managers of engineering projects, can usefully learn from the history of steam locomotives.

One is the difficulties associated with novel designs. The novelties do not need to be particularly extreme. Nearly all new engineering designs suffer from teething troubles. But in addition, there are sometimes weaknesses that manifest many years later and affect every single example of the type.

A good example of this is the Merchant Navy class, introduced in 1941. In 1953, a crank axle broke, due to a design flaw which required the withdrawal of the entire class, initially for inspection and eventually for complete rebuilding.

All thirty members of the GWR King class also had to be withdrawn and repaired due to a fault long after they came into service. This was in 1956, nearly three decades after they were introduced. Like the Merchant Navy problem, it was due to fatigue cracking, in this case of the main frames.

The temporary withdrawal of the Merchant Navy class, meant that substitute locomotives had to be drafted in from elsewhere, resulting in some novel appearances. The loss of the GWR Kings caused less of a difficulty as Castle class locomotives could take over, but the examples illustrate the risk of putting all the eggs in one basket.

It is obviously not a lesson that was understood by those who were responsible for the decision to replace the entire surface line fleet of London Underground by a single class of stock between 2010 and 2016. Given that these trains are meant to have a thirty year life, it will be interesting to see how they fare.