As one of the eight original German Type IX submarines, later designated IXA, U-37 had a displacement of  when at the surface and  while submerged. The U-boat had a total length of , a pressure hull length of , a beam of , a height of , and a draught of .
The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of  for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of  for use while submerged. She had two shafts and two  propellers.