XE class: used in the Far East against Japan, where they carried out a number of attacks and special missions. Welman submarine: a single-person submersible widely considered a failure.[40] Welfreighter: a Station IX-developed special operations submersible with two crew and up to four passengers, designed to resemble a motorboat when surfaced. Over 100 were produced, beginning in September 1944; the extent of operational use is unclear.[41][42]