Appropriately enough, it's a place called Midway Island, which is part of the Marine Corps Base at Quantico. You may want to stop before the base at Triangle, VA. It's the home of the National Museum of the Marine Corps if that holds any interest.
About 130 miles.
Towson, MD
It is 43 miles taking SUITLAND PARKWAY, from D.C., to MD-4 SOUTH, and then MD-4 SOUTH to Prince Frederick.
The distance between Phoenix, AZ, and Frederick, MD, is 2,292 miles and will take about 34 Hours to drive.
Richmond, VA
Procious
According to trueknowledge.com, it is 43.5 miles from Frederick, MD to Baltimore, MD.
Youngdale, PA is your halfway point.
about 50 miles
Frederick MD forecast week of Jan 25,2016
Unionville, PA
You can buy its at Willys in Frederick, MD