The Pennsylvania Railroad's class HH1s comprised a single 2-8-8-2 type steam locomotive. Unlike most Pennsylvania Railroad steam locomotives, it had a wagon-top boiler. It was built by the American Locomotive Company (ALCO) in 1911. For 17 years, the single HH1s served as a helper until 1928. It had the road number 3396 and was subsequently scrapped after it was taken out of service in 1928.