I have a few of those.
My first TL involved a design from Ultimate Admiral Dreadnaughts. At one point in the designer, one could mix and match structure hull and equipment. Hence why this battleship design got in my head. At the time, I was thinking "how can one do a 21 guns salute most effectively?"
The answer, according the design I came up with, was a progression for some of the Tillman designs. 17" guns in 7 turrets for 21 guns. 76 caliber... 170,000 some tons, 37 knots... At the time, I figured the length pushed out to like 1500ft long by 150 or so ft wide. Yeah, pipe dream territory, but its on another forum.
Another involved Japan owning eastern Siberia and Kamchatka to a point, where I used designs inspired by RTW2 play through for Japan. Kongos with 20" guns, Shinano class with 15 18" guns... Yeah, that one is a word doc, never put it on the net.
But the very first Timeline of sorts I made was something I thought up as a kid. Involving massive space exploration and tech advancement so as to push humanity to the stars by like 2010 or so... Muse died for it long ago, had it sitting at 120 pages last I recall. Was also the one where I would draw out the spaceships to a simple scale of 1":1mile. There were ships I drew that in my mind, were close to 33 miles long [3 sheets of notebook paper taped together end to end].
Anyway, most of those first TLs were pretty much in space bat territory, but as a child, I dreamed big and had an extensive imagination. Hard not to while on a farm.