Smirky, I stand to be corrected but to my knowledge the Mk 5 wasn't used in ASW 'dipping sonar' role, it was for Commando Assault, anti-shipping and SAR use so a 'cable-out' indicator wouldn't have been required
Some HU 5 didn’t have the empty sonar bay, so they had a great big uncomfortable box in the Fwd left cabin to sit on, that housed the junk that would have been in the bay if I remember correctly.