U.S. Navy Seaman Matthew Ramer looks through binoculars for small boats while crossing the Strait of Hormuz aboard USNS Walter S. Diehl, May 5, 2005. Ramer is a master at arms assigned to Mobile Security Detachment 24, aboard the Diehl, which is currently in the Arabian Gulf conducting refueling operations with the fleet in support of anti-terrorism efforts in the Horn of Africa region. U.S. Navy photo by Petty Officer 1st Class Aaron Ansarov
USNS Walter S. Diehl
Info on USNS Walter S. Diehl here and on the Henry J. Kaiser class of fleet oilers here.
Update: Some background info on Mobile Security Detachments here.