British W-class submarines were built for the Royal Navy as experimental boats, and were based on the French Schneider-Laubeuf design.
This design was modified very heavily by the Navy, which resulted in removing the issues of the previous design; the main difference was the removal of the drop-collars. The W-class subsequently performed significantly better, offering brilliant diving control and far more efficient venting and flooding systems.
Only four of the W-class submarines are constructed, being delivered between 1913 and 1916. In fact, the first two submarines took 15 and 17 months to build, which was hailed as a remarkable feat compared to other submarine building times during World War One.
The four W-class submarined were eventually transferred to the Italian Navy in 1916. W4 is thought to have been sunk by a mine after its transfer, while all three of the other submarines were striken after the war.
See the table below for more information on the characteristics of the W-class submarine:
W-class submarines statistics:
| Number completed before 1919 | 4 |
| Number completed after 1919 | 0 |
| Lost in action | 0 |
| Lost accidentally | 0 |
| Prototype date | 1915 |
| Surface tonnage | 340 |
| Submerged tonnage | 508 |
| Length | 171 feet |
| Engine | Diesel |
| Horsepower | 650 |
| Screws | 2 |
| Surface speed | 13 knots |
| Submerged speed | 8.5 knots |
| Torpedo tubes | 18 inches |
| Number of torpedoes tubes | 2 |
| Guns | 1 |
| Crew | 19 |
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