A 2¼ square film negative. The Type 12 frigate Yarmouth (1959) in No. 2 dry dock in Rosyth Dockyard. A very close view of the internal arrangements of Hull Outfit 20 Type 174 sonar between 15 and 19 stations. The covering dome and the main transducer panel has been removed to show the rotating mechanism. The photographer is on the floor of the dock under the unit looking up, forward and to port.