You Navy guys always ran a tighter ship than the Air Force.
Seaman Flowers hand carried his NAF Tech Control 55-1 reports to our Comm Center and often stopped to visit with us in the Tech Control. We didn't have any gear or documents we had to scrub or cover. We couldn't visit the NAF facility because it was loaded with bays of crypto gear and other sensitive items in the open. I got to see it on an open house once and also visited the NSGA station a couple of miles away.
I found out years later that my background investigation may have been easier because my father and grandfather already had security clearances although not cleared for TS as far as I know.
“Secret” clearances are fairly universal in the USN. Even USPS carries “Secret” snailmail.
‘Curious where that NSGA was located.
As to difficulty, my USN Dad was strafing, bombing, depth-charging and torpedoing the Japanese in the SW Pacific as an officer.
I was a mere enlistee, whose many addresses and personal referrals were questioned, then even THEIR neighbors were checked!