In the episode 'Affliction' genetically-engineered Klingon augments use a Klingon attack ship  to mount a raid on the Enterprise NX-01. The ship was designed by John Eaves, who was originally told it shouldn't be instantly recognizable as a Klingon ship. As the design evolved it becamse clearly Klingon but it is one of the smallest Klingon ships we ever saw. The model is just under 4" (10 cm) long.