In 1944 though: From: HyperWar: NEPTUNE: Training, Mounting, The Artificial Ports [Chapter 7] and possibly duplicated on: 211
There's this file at TNA: "Swan" scheme reports | The National Archives Reference: WO 199/836 Description: "Swan" scheme reports Date: 1945 May -July WO 199 is the series for EXERCISES AND TRAINING under HOME FORCES