When it had finished being the prototype 146-100, it was sliced up, had bits inserted and was fastened back together again to make the prototype 146-300.
A previous Hatfield prototype (as the 146 was) had maybe given experience in this area.
https://www.google.co.uk/search?q=de...t8rKVeICqTU3qM:
I understand the repairs took just a few weeks.