Anyone have any idea how noisy an unpowered, towed, autogyro would be, from the perspective of the pilot? Rotor and slipstream?

The reason I ask is that these aircraft would normally only be operated in conditions of good visibility, when altitude would provide a meaningful increase in visual detection range of targets and surface-threats, and only after a 360 deg sweep for visual and acoustic contacts, so the chances of being surprised by an enemy warship would seem to be be minimal.

The only reason for a potential crash-dive then would seem to be the threat from patrol aircraft. The conning tower of a surfaced U-Boat was brimming with lookouts, but their ability to detect the sound of approaching aircraft would have been be severely limited by the presence of the adjacent engine induction and exhaust systems. Would the autogyro pilot be able to hear an approaching aero-engine?

Also perhaps worth mentioning that a U-Boat's response to an airborne attack was not always necessarily a crash-dive. Later models were bristling with Flak, and several patrol/attack aircraft were lost to them, including a Liberator of 200 Sqn RAF, who's captain was later posthumously awarded with the VC, solely on the testimony of the U-Boat's crew.

https://en.wikipedia.org/wiki/German_submarine_U-468

A quick internet search suggest a speed range of 15 to 40 knots and that they were not deployed anywhere with enemy air cover. So their practical usage was very limited. Apparently only one freighter was sunk with their help. What I did find interesting is that the concept is being looked into by the US right now for use with surface ships. I don’t know any more than that L3 is exploring their usage at much greater altitudes. Several thousand feet was suggested. Certainly an unmanned platform able to maintain position for long periods using modern sensors possibly even armed sounds attractive.

A superb full video of the Focke Achgelis Fa330 Bachsteltze (Water Wagtail) ...
 

There's a great full video of the Focke Achgelis Fa330 Bachsteltze (Water Wagtail) , in action from 1942 WW2 on YouTube now enjoy :-) TFC ;

Autonomous drones can be posted out around ships to help detect any incoming. Some could deploy as bogus targets .
Great video clip… after weeks in a stuffy smelly sub the airborne lookout certainly gets his share of fresh air and a good look at his home from a different perspective.

While I certainly wouldnt want to be the pilot in one of these are the dangers not a little overblown about crash diving.

If the sub doesnt have radar how is it going to crash dive without the alert from the guy in the gyro copter..

He could see a destroyer probably ten miles away whereas on t he sub its two miles away. Plenty of time to recover to the sub, perhaps not to stow the contraption, but time for the pilot to descend and report and then crash dive

https://cimg8.ibsrv.net/gimg/pprune....ef8964b28b.jpg
Fa330 land trials at the AFEE RAF Beaulieu. The trailer is the floor of an Airfield Control Caravan and the Jeep towing is the Hafner Rotabuggy minus the rotor and tail.
https://cimg2.ibsrv.net/gimg/pprune....160b5adf1f.jpg
The Fa330 sea trials at the AFEE used a launch from nearby RAF Calshot. Would this qualify as the UK's smallest aircraft carrier?

Did a check against the list in "Wings on my Sleeve" and was surprised to see that Winkle never actually flew the Fa 330, must have been about the only captured Axis platform not in his logbook.

I suppose technically the speedboat in the James Bond film "Moonraker" which launched a powered hang glider before crashing over a waterfall might qualify - it was owned by Eon Productions who are a UK company! :p

but once they surfaced, and needed to look for the pilot, they could always launch the gyrocopter

...oh wait