No problem Dave. They were projected to be 136.9m long which converts to just over 449ft.

As for their role, in the book they are grouped with 'Minenraum(mutter)schiffe', which translates as 'Minesweeper Mother-ship'. As you know the Trident model of 'B' has 9 small boats aboard, so perhaps they were mini-minesweepers carried by the larger vessel?

If you like, I can email you screenshots of the pages from the book?