U.S. Passport Designations
I am curious about what the letters "SP" might mean when they precede a US passport number. I found a passenger list for the ship the US President Cleveland dated 1957. The passengers embarked in Manila, went on to Yokohama Japan and then San Francisco. The names of my grandfather, Howard H. Boyce, my step-grandmother Maxine Boyce,
and their son Frederick M Boyce are listed. They all have passport numbers preceded by SP, ie SP - 54187. Howard had previously worked for the US Treasury and later the American Institute of Research, but I don't know why he would have been in Manila in 1957. He would have been about 50 years old. I'm wondering if it might be a military or government designation? How could I find out more about their time in the Philippines?