The submarine was then given the task of crossing the Skagerrak and laying a minefield in the Kattegat. This operation, named FD7, was part of the Norwegian campaign of early 1940. Lonsdale's superior, Captain Jocelyn Slingsby "Jock" Bethell, commanding 6th Submarine Flotilla, considered the operation too dangerous for a large mine-laying submarine. But he failed to persuade Admiral Max Horton to reconsider his orders, and "Seal" sailed from Immingham on 29 April 1940.