SM U-77[Note 1] was one of 329 submarines serving in the Imperial German Navy in World War I, engaged in commerce warfare during the First Battle of the Atlantic.

The submarine was powered by two 900 metric horsepower (660 kW; 890 shp) engines for use while surfaced, and two 900 metric horsepower (660 kW; 890 shp) engines for use while submerged.

[2] When submerged, she could operate for 83 nautical miles (154 km; 96 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 7,880 nautical miles (14,590 km; 9,070 mi) at 7 knots (13 km/h; 8.1 mph).

She had a complement of thirty-two (twenty-eight crew members and four officers).

[4] U-77 was thought to have sunk off Dunbar, Scotland in May 1916 as a result of a mine handling accident.