Small Patrol Submarine
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This class was built primarily for A/S training and to replace the 'H' class which by this time were considered very much past their best. Originally not intended for war but forced into the role by hostilities and the fact that they could be produced very quickly.
In theory they were in all aspects inferior to almost all foreign submarines, their performance and success during WWII proved otherwise.
The principal design of the Unity Class were retained in this group. Additional equipment made it necessary to remove the external bow tubes but the high bow was retained in the first six boats of the group. The boats which were built with a finer bow had a slightly longer overall length and larger forward hydroplanes were fitted to improve control.
The need for these boats to be used operationally decreased after hostilities ceased in the Mediterranean and stopped altogether at the end of WWII. Consequently they were used in the role for which they were originally intended, Anti-Submarine Training boats.
192.33 oa Undaunted, Union, Urchin, Urge.
196.83 oa Umpire and Una.
196.83 oaUnbeaten and Unique after modification.
Paxman or Vickers on others.
General Electric motors 825 bhp
2 x 0.303 inch Lewis or Vickers MG.
4 x 21 inch bow tubes, 4 reloads.
Unbeaten and Unique after modification carried 1 x 3 inch/45 QF MkI in place of 12pdr/12cwt HA.