German submarines leaving Heligoland towards the United Kingdom according to the Weekly appreciation of matters of naval interest No.13 week ended 15 March 1919

An item reported that of the five German submarines departing from Heligoland destined for Harwich, England as reported in the last appreciation just 3 three arrived. One, probably the U.B. 133 lacking engines and crew was picked up by a Dutch trawler and brought to IJmuiden, Netherlands and the fate of the fifth one unknown.

Source

The National Archives, Kew Gardens, England CAB-23-76-100