The D-4 class was designed by John Eaves as a earlyer version of the later D-7/K'Tinga class. This ship was planned for Vorok's battle cruiser in Star Trek Enterprise "Unexpected" but at the end never used.
design scetch by John Eaves (startrek.com)
I bought the Klingon D-4 resin kit in 1/1400. It's a very fine detailed model with 15,3cm in length. The kit contains the rods for the bottom of the neck. I corrected this kit with very thin steel braces in front of the grills and at the end of the wings.