From the 18 July 1857, Baltimore Sun: The United States sloops of war Germantown and Preble (practice ship) dropped down from Norfolk, on Wednesday, to the naval anchorage.
"The latter is expected to sail on a practice cruise in a few days.
"Lieut. Alexander M. DeBree has been detached from U.S. receiving ship Pennsylvania, and ordered to the Preble."
So, these are two ships he served on while in the U.S. Navy. The Pennsylvania was an old ship-of-the-line based at Norfolk and the Preble was being used as a practice ship for the USNA.