The Mighty T

The Pennsylvania Railroad's 52 T1 class duplex-drive 4-4-4-4 steam locomotives, introduced in 1942 (2 prototypes) and 1946 (50 production), were their last-built steam locomotives and their most controversial.
They were ambitious, technologically sophisticated, powerful, fast, and uniquely streamlined by Raymond Loewy. However, they were also prone to violent wheelslip both when starting and at speed, complicated to maintain, and expensive to run. In 1948, the PRR vowed to place diesel locomotives on all express passenger trains, leaving unanswered whether the T1's flaws were solvable (Wiki).