These boats were built to a French Schneider-Laubeuf design, their French ancestry being obvious in the shape of the hull.
The Admiralty eventually decided against the French design after a visit to Toulon, though an order for four boats was given to Armstrong to keep an agreement to order two boats a year from them.
The class name was derived from the builders name (Whitworth). Being complete failures as they were best suited for service in the Mediterranean the boats were sold to the Italian Government in 1916.
Neither of these boats served in the Royal Navy and were transferred to the Italian Government in August of 1916. W3 was discarded in September of 1919 and W4 was sunk by mine off Capo Rodoni in August of 1917.
2 Electric Motors 480hp.
8.5 kts sm
4 x 18 inch in external drop collars.