thumb|300x300px|Union Pacific Challenger No. 3814 was one of the first examples of a 4-6-6-4 locomotive In the Whyte notation for classifying steam locomotives by wheel arrangement, a 4-6-6-4 is a railroad steam locomotive that has four leading wheels followed by two sets of six coupled driving wheels and four trailing wheels. 4-6-6-4's are commonly known as Challengers.
thumb|300x300px|Union Pacific Challenger No. 3814 was one of the first examples of a 4-6-6-4 locomotive In the Whyte notation for classifying steam locomotives by wheel arrangement, a 4-6-6-4 is a railroad steam locomotive that has four leading wheels followed by two sets of six coupled driving wheels and four trailing wheels. 4-6-6-4's are commonly known as Challengers.
A similar wheel arrangement exists for Garratt locomotives, on which both engine units swivel, but is referred to as 4-6-0+0-6-4.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).