[Milsurplus] SRR-11 GI users, info please?

[Unserviceable but Repairable]

SRR-11 the 14-600kc sub-mini-laden rx by RCA.  But that's unneeded for 
a Navy submarine radio man on duty in the 60s & 70s.

Think most or all subs had these to receive VLF attention-getters fm 
Jim Creek then.  While undersea.

My question relates to background noise arising from rf-input.  Did it drop 
materially when the sub submerged?

  Tnx

     'rm