Surface warfare against merchant shipping is variously called guerre de course, cruiser warfare, commerce raiding, or in German, handelskreig. The Royal Navy dominated the ocean in World War One, and surface warfare against allied merchant shipping was made nearly impossible. The handelskreig was conducted by U-boats.
On the surface, the German navy resorted to using adapted merchant ships, armed with hidden guns and torpedo tubes. The most successful of these were fairly anonymous but speedy freighters, who could plausibly disguise themselves as neutral or allied ships. They took their fuel – coal – from their prey, along with any supplies that would be useful to the German war effort or themselves. They were also equipped with mines to drop in shipping lanes.
The Vienna of Leith was interned in Hamburg in 1914 and the Shetlanders in the crew were in Germany for the duration. The Vienna became the Meteor and sank the British Armed Boarding Steamer Ramsey in the Moray Firth in August, 1914. There were Shetland sailors in that crew as well. The Meteor was scuttled as more powerful forces closed in.
The Möwe (Seagull) was more successful. One taken vessel, the Rhodanthe of London had three Shetlanders in the crew. One, William Robertson of Baltasound, was a gunner. Some years later in 1935, another crewman T G Lawler spoke to the Western Australian newspaper –
We had a seven pounder on board, but it was hopeless to fight. She was armed to the teeth. We hove to …
That was on 4 March 1917. Unlike U-boats, raiders could hold large numbers of seamen prisoner, and sailors were more likely to survive attack by a surface raider. The Rhodanthe crew endured 21 months custody. That meant crowded conditions, indifferent food supplies, and surviving a firefight with the New Zealand Shipping Company vessel Otaki. The Möwe then returned home damaged, and the seagoing part of the ordeal was over. In Germany there was a hero’s welcome and a film of the ship’s exploits.
The most successful raider was the Wolf. Although not a fast vessel, it had a Freidrichshafen spotter plane to assist. She left Germany on 30 November 1916, and embarked on an epic 451 day voyage. On 24 February 1918 Captain Nerger returned home to Kiel, and was awarded the Pour le Mérite. Among the 467 prisoners on board were two Shetland sailors. John J Moncrieff, Taing, Trondra, chief officer of ss Jumna, taken on 1 March 1917, was one. The other was a Lerwick emigrant to New Zealand. Peter Isbister was the second officer of ss Wairuna, made prisoner on 2 June 1917, of Sunday Island in the Pacific.
Peter Isbister kept a diary. It got destroyed at Kiel, but on a visit to Shetland in 1919 he recounted his story to the Shetland News newspaper. He spoke about how he was made prisoner, about being accommodation with mines stored close by, and about how scurvy was prevalent among the prisoners when they made Kiel. And about how Captain Nerger circled through the North Atlantic on the way home, and passed within 240 miles of Shetland.