Group One and Group Two
These boats resulted from an Admiralty theory that submarines should have the capability to operate with the main fleet, this obviously required a much higher surface speed than submarines of the time were capable of. These submarines would be referred to as 'Fleet Submarines'.
On completion they were only able to achieve 19 knots which was deemed to be too slow to work with the fleet and as a result they were reclassified as 'Overseas' Submarines.
2 Electric Motors 1,350 hp.
9.5 knots sm
1 x 3 inch QF, 1 x 2 pdr pom-pom.