SM U-155, a Type U 151 submarine launched in 1916. It was first known as the merchant submarine Deutschland from launch.
After making two voyages as an unarmed merchantman, she was taken over by the German Imperial Navy on 19 February 1917 and converted into U-155, armed with six torpedo tubes and two deck guns. Commissioned as U-155 on 19 February 1917. Shows some wear and use, yellowing, and few pencil marks on back. Approx 5 3/8" x 3 3/8". Check out my other WW1 postcards.