There is quite some lively debate as to which vessel she is, either U-122 or U-123 or even UB-122 but the original story of how she got there remains the same.
Post war the surrendered U-boats were acquired by scrap companies to break up. Twenty Three U-boats were towed from Harwich to the Medway and one of them grounded in Humble Bee Creak, the rest were stopped near by and had their engines and generators removed.
Unfortunately for the Scrap companies there was so much Scrap metal available at the end of the war that there was no money in it and the market quickly collapsed. The Boats remained on the marshes until World War Two when the other more accessible vessels were taken apart for their valuable metal.
This vessel though remains upon the marshes where she lay, her nose cone removed and resting in front of her so she cannot be used as per Versailles agreement and her hull slowly rusting away.
U-122 and U-123 were both built in Hamburg and launched in December 1917 and January 1918 respectively, both were UE II type Mine layer submarines.
Each had a crew of 36 men and 4 officers with a top speed of 11.5 knots (7 knots submerged)
U-123 was Commanded by Oberleutnant zur see Karl Thouret whose previous commands had been U-79, U-78 and UB-93.
U-122 was commanded by Kapitanleutnant Alfred Korte and was the only one of the three Vessels to score a "kill." The Icelandic vessel Njordur (A fishing trawler of 278 Tonnes) was shelled and sunk on 18th October 1918.
Which ever vessel she is, this interesting anomalie lays resting on the marshes and is little known to the people of the Medway towns. For the history geek like me it is truly fascinating but for many it is a historic irrelevance doomed to continue its slow decay, a grim fate for the last of her kind.
See also http://www.squidoo.com/ww1-uboat-sub-wreck and also http://www.uboat.net/