@revelette2,
• I've had had many talks with someone (a friend of my late mother-in-law), who had been on a GDR-boat, which did the same job as we did ... and which we had to approach a couple of times very close (in international waters) to read the id-number (they stayed mainly at anchor, changed the boats at night and during bad weather).
• We were missed by a few yards by a surfacing Danish submarine - they did the same job we did, neither knew of each other. (That not gave some "water disturbances").
• When we were on duty as a "picket boat" (four boats, minesweepers, were doing this job over roughly six weeks: one "on vacancy", one on duty, one "picket boat", one on the way back from or to duty), we got a "special job": taking a "passenger" on (sic!) the three-mile-border of the GDR. That stretched our picket duty from 24 hours to four days ... since we had a) to wait for a dark, rainy night, b) get the order to go there from a "higher command".
Since I was doing the navigation, I was calculating all and everything. I was 100% sure that we clear of the three miles zone, when the outlook noticed "something black, obviously sinking, waving". Inside the three mile zone. So, I made a fatal navigational error, we got our passenger aboard, no-one seemed to have noticed us (it took them nearly one until the 'shadowed' us).
I noticed in the log, with a position outside the 3-mile-zone: passenger, unknown name, aboard at position so-and-so.
This person was immediately covered with a blanket, stayed only in the captain's cabin, spoke English with accent, left our boat a couple of hours later, on sea, going on board of a yacht with no flag or identity number/name.
What I noted in the log as well. (I had had a discussion with the captain, why I did it. He followed my argumentation.)
Two days later, we got visitors just minutes after having arrived in the harbour. One spoke German, identified himself as someone from the German military intelligence; the other spoke German with accent, didn't show his ID-card nor tell his name. They
convinced me that unfortunately I had spilled some ink over that page of the log.
• We all were highly praised by our squadron commander and the admiral of the mine fleet (which we didn't like a lot, because we had to wear parade uniform - but got two extra days free, which was good). And got weeks later a new similar job in the North Sea and North Atlantic. (Actually, it was only planned for four days. But a Dutch frigate had had engine trouble - so we had to start earlier. And an English destroyer had had something else - so it lasted longer.)
But this job really was fun_ following a Russian "trawler" from the Kiel canal to the English Channel, then up the English east coast to ... well nearly where icebergs commonly can be seen [I didn't have any good charts for that region at all!]
That "trawler" had an ocean of antennas, instead of 67 crew members as officially noted, there were more than 150 -I'd counted 150+ every morning, when they made their morning gymnastics on deck. When they did so, we circled around them and played the "International" on our loudspeaker system.
... ... ... ...
) ... and became 'upgraded' in my security within days.