1903 - 1906: B Class
In an attempt to improve on the A Class shortcomings, a larger vessel was designed some 40 feet longer than A1, 10 inches more in beam, and 100 tons more displacement. This was the start of the B Class of which eleven were built between 1903 and 1906. The B Class were the first submarines to be fitted with deck casings. Surface performance was improved over that of the A Class, but underwater performance was substantially the same.