The Arrow is a family of electric multiple units ordered by the PRR in the sixties. The first batch of 35 was built in 1968 and is called Arrow I. Their bodies were of monocoque design with load-carrying walls of corrugated stainless steel. Every car was powered by four 175 hp traction motors which were fed by Westinghouse silicon rectifiers. Due to their unreliable control equipment, they were out of service by 1980 and replaced by Arrow III cars. In 1987 and 1988, 30 were rebuilt to Comet IB cab cars and trailers.

In 1974, Penn Central received 70 Arrow II cars which were arranged in married pairs. Now, only one of the two cars in each pair had a pantograph, but still every axle was powered. These were retired starting in 1997 and nearly all had been scrapped by 2001.

The Arrow III arrived in 1977, of which 30 were built to operate as single cars and 200 were built to create pairs. These were rebuilt by ABB between 1992 and 1995 where they received three-phase traction motors and GTO thyristors. Since the new traction motors were a bit more powerful, the married pairs lost both traction motors in the outside truck of one car. The Arrow III is still in service, but they are currently being replaced by Bombardier MultiLevel EMUs.