SMS Seeadler (Ger: sea eagle) was a three-masted steel-hulled sailing ship. She was one of the last fighting sailing ships to be used in war when she served as a merchant raider with Imperial Germany in World War I. Built as the British-flagged Pass of Balmaha, she was captured by the German submarine SM U-36, and in 1916 converted to a commerce raider. As Seeadler she had a successful raiding career, capturing and sinking 15 ships in 225 days until she was wrecked, in 2 August 1917, in French Polynesia.

The ship was launched as Pass of Balmaha by Robert Duncan & Company, Port Glasgow, Scotland, on 9 August 1888 as a steel-hulled ship-rigged sailing vessel measuring 1,571 gross register tons (GRT). She was 245 feet (75 m) long, 39 feet (12 m) in beam and with a depth of 23 feet (7.0 m). Delivered in the following month to the ownership of David R. Clark, a partner in Gibson & Clark, Glasgow, she was registered at that port with Official Number 95087 and signal letters KTRP.

In February 1908, Pass of Balmaha was sold at Leith by Gibson & Clark for £5,500 to The River Plate Shipping Company Ltd of Montreal. Her port of registry remained Glasgow, but she was managed by American interests in Boston, Massachusetts. By 1910, she had been transferred to the Ship Pass of Balmaha Company Ltd, Montreal, and under the management of George I Dewar, Toronto. Both of these companies were controlled by American shipping and lumber interests.

Soon after the outbreak of World War I in 1914 Pass of Balmaha was transferred to the neutral United States flag and registered at Boston in the ownership of the Harby Steamship Company Ltd of New York, part of the Harris-Irby Cotton Company.

Pass of Balmaha was captured by U-36 in the North Sea in 1915 under somewhat peculiar circumstances. She departed from New York Harbor in June 1915, bound for the Arctic port of Arkhangelsk with a cargo of cotton for Russia. She was intercepted by the British auxiliary cruiser Victorian off the coast of Norway. Victorian's captain led a boarding party to inspect the cargo for contraband. The British captain found reason for suspicion, and ordered Pass of Balmaha to sail to Kirkwall in the Orkney Islands for further inspection. A prize crew of an officer and six marines was left aboard to ensure compliance.

The British also ordered the neutral American colours struck and replaced with the British flag, against the will of Pass of Balmaha's Captain Scott, who realised that this would mark the ship as a belligerent. Soon after, U-36 intercepted Pass of Balmaha. To avoid being impounded, Scott hid the British prize crew in the hold and replaced the Union Jack with the Stars and Stripes. The commander of U-36, Captain Ernst Graeff, was not entirely convinced by this ruse and ordered Pass of Balmaha to sail for Cuxhaven for inspection. Since U-36 was short of personnel, the German prize crew consisted of only one man, Steuermannsmaat (Mate) Lamm. A German ensign was left aboard. Scott and his crew, resentful of what they perceived as British meddling, kept the British marines locked in the hold.

Pass of Balmaha reached Cuxhaven without major incident, and was boarded by a German inspection party. Captain Scott then revealed the British prize crew to the Germans, who took them prisoner. For their cooperation, the Americans were allowed free passage to a neutral country, but Pass of Balmaha became property of the German Navy.

By 1916 the Allies had blockaded German warships in the North Sea, and any commerce raiders that succeeded in breaking out lacked foreign or colonial bases for resupply of coal. This gave rise to the idea of equipping a sailing ship instead, since it would not require coaling.