Quoting the late, great and dearly-missed John Tilley:
"To begin with, it isn't a Coast Guard vessel. The USCG has operated quite a number of tugs over the decades, but none of them have resembled this one. It was originally issued back in the fifties, simply as a "tugbboat"; the CG decals came much later. I think its original incarnation included an electric motor. It sticks in my mind that, in at least one of its appearances, it had the name "Carol Anne" on the box. That, however, may be a figment of my Halfzeimer's-afflicted memory. (My wife asserts that, though I don't have Alzheimer's Disease, I do have Halfzeimer's - and she has the other half.)
"I'm not aware of where, if anywhere, Lindberg got the plans for it. It's not a bad representation of a typical wood tug of, say, the 1920s through the 1950s - bearing in mind the state of the art as it existed in the fifties.
"That's about all I can offer; sorry."
Here's the thread, if you're interested:
https://cs.finescale.com/fsm/modeling_subjects/f/7/t/123959.aspx