They were actually very lucky that the crane wasn't up to the weight - if they had had a capable crane, then they wouldn't have found out at that point.....
Where I worked,for very complicated reasons involving take-overs and bankruptcies, we made transport cases for torpedoes for a while. These had internal suspension and were supposed to protect the torpedo from damage if it was dropped on a concrete dockside when being loaded. We had an "Inert Dummy", a genuine casing, with a filling to simulate the weights of the real innards, so that we could check that it would fit properly, etc.
One morning, completely unannounced, two Land Rovers full of Naval MPs turned up, with a low-loader containing another Inert Dummy. "You will swap the one that you have for this one - now!"
They refused to discuss the reasons behind this.
I like to think that we might have just had a torpedo with a live motor*, but, knowing the Scampton Grand Slam history, I was happier when the swap had happened - if we even had the right one then, of course......
*The motor was a gas turbine running on Otto Fuel - that going off would have been exciting enough...
..but a 300kg warhead was another matter..
..and from outside, it was impossible to tell, except for the markings, if they were right.......