I did it for 10 years as a radio officer in the merchant. Once you're reasonably competent the letters just form in your head. It's a bit like speaking another language.
In audio morse there's a plateau at about 12 words per minute where your brain switches from hearing dit dah dit as 3 separate sounds to the letter R fully formed.
After that you can lag enough to be able to write whole words at once rather than separate letters
+ VA