NOT TO SCALE My rather clumsy drawing to show you the relevant approximate distances in an 'A' Class boat.
 A = Periscope depth from KEEL to Top of Fin 55 feet.
Radio HF/MF aerial  B = Top of fin to top of raised periscope approx 15 feet
 C = Distance above sea level 1 foot depending on weather of course - have to see but not
be seen!
 D = Distance below sea level of VLF receiving aerial approx 15 foot. See Note below.
      C  E = Overall APPROXIMATE distance = 70 feet
Insulator
B Note: Rugby can be received with aerial 22 foot below
surface at a range of 2000 miles.
SEA LEVEL
D
FORE AND AFT WOUND LOOP
Aerial mast with fairings
PORT AND STARBOARD
A Periscope WOUND LOOP
E
FIN
Skipper
Control room deck level
Depth of well same as height of scope Periscope well when 'scope is fully lowered
above top of conning tower fin