A Type UB II submarine, UB-39 had a displacement of 274 tonnes (270 long tons) when at the surface and 303 tonnes (298 long tons) while submerged.

The submarine was powered by two Körting six-cylinder diesel engines producing a total 284 metric horsepower (280 shp; 209 kW), two Siemens-Schuckert electric motors producing 280 metric horsepower (210 kW; 280 shp), and one propeller shaft.

When submerged, she could operate for 45 nautical miles (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 6,450 nautical miles (11,950 km; 7,420 mi) at 5 knots (9.3 km/h; 5.8 mph).

She had a complement of twenty-one crew members and two officers and a 42-second dive time.

She was commissioned into the German Imperial Navy on 29 April 1916 as SM UB-38.