The CH-3E and CH-53s were rejected by the Royal Navy as they would not fit on the Escort Cruiser's lifts according to The Admiralty and the Helicopter.
Here's the relevant passage:
I would like to add to Fred Hoskins’ excellent presentation on the Sea King, to point out that procurement doesn’t always happen like that, the Chinook being a good example. I was sitting quietly in OR, minding my own business, my boss having spun off to have a nervous breakdown, when Wg Cdr, as he was then, Bill Croydon, popped his head round the door and said, ‘We’ve got a little bit of spare money, Hugh, how many Chinooks do you think we ought to have?’ As we’d cancelled them twice already, I said, ‘Well, it’s got to be an order big enough so that cancellation would cause a riot; we’ve got to have at least two squadrons - nine in each - so we’ve got to have eighteen.’
The problem, of course, was holding off competition for the spare money. We did that by persuading the army to insist that a particular gun had to be lifted, one which we knew the CH-53, the only sensible alternative, couldn’t manage. Then we shot round to the navy and said, ‘If you get in our way (because they wanted us to buy the Merlin), we’ll screw the Merlin up.’ Meanwhile, the money surplus grew and the Minister called for my then boss, John Maitland, to talk to him about helicopters. We produced two diagrams to sell our case. One showed cost against payload, the other showed the relative size of the various aircraft in contention. Having ‘cut the rotors off’, we were able to show that the Chinook really wasn’t very big, certainly smaller than the Merlin, and that it was very cost effective. The next thing was a note from the Minister saying, and I quote, ‘The purpose of my committees is to protect me from a bad decision. In this case, I am absolutely convinced that I don’t need protection; we are going to buy the Chinook.’ Now that is another way of procuring a major piece of equipment, so don’t put all your faith in doing it with staff papers. A bit of luck and fast footwork can often absorb a budget deficit!
From RAF Historical Journal 25:
https://www.rafmuseum.org.uk/docume...Journal-25-Seminar-Helicopters-in-the-RAF.pdf
The bit about a Chinook being smaller than a Merlin with the rotors folded is absolutely true, by the way. I didn't believe it myself until I saw the drawings that proved it.