British W-class submarine

The W-class submarines were built for the Royal Navy as experimental boats. They were based on a French Schneider-Laubeuf design. The design for "W3" and "W4" was heavily modified to meet Royal Navy requirements, overcoming some of the deficiencies of the 'off the shelf' design. In particular, the drop collars were removed in the later boats.
Only four W-class submarines were built from 1913 to 1916. The first two boats took 15 and 17 months to build, which at the time was a remarkable feat compared to other building times.
The W class had very good performance, with excellent diving control and efficient venting and flooding systems. The class did have problems with habitability, but other than that, they were good submarines.
All four of the W-class submarine were transferred to the Italian Navy in August 1916, where they retained their numbering. 