Reliant was the first new official Starfleet ship ever created. Interestingly, the original design had the nacelles above the saucer like Enterprise, with two torpedo pods under the hull. However, the person approving the designs signed off on the blueprints upside down, and they ended up building the filming model the way we know it today. Something I learned making this model, is that the Miranda Class doesn’t use the same saucer as the Constitution, it’s actually slightly smaller.
A common misconception about the Miranda is that’s she’s smaller than the Constitution. She’s actually about 90% of the Constitution’s volume, and is actually comparably armed. 18x phasers and 2x torpedoes for the Constitution, and 16x phasers and 4x torpedoes for the Miranda. Miranda is actually better armed if you believe in the mega-phaser idea, though I don’t personally.