it was designed to test insulators to protect aircrafts, vehicles and electronic equipment against lightning.
I have to say that I haven't even googled whether this is correct or not... but this more than likely to test the effects of EMP rather than lightning strikes. A lightning strike would have been an unusual occurrence, and the loss of one single machine / weapon would have had a negligible effect. To lose the whole military capacity would have been not such a good thing.
We were doing EMP tests in the UK...