Td racer:
I've always heard the 707 Dutch Roll behavior was really bad (with regard to what aterpster wrote - I hadn't heard the 727 was as bad or worse than the 707 - not disagreeing, just relating Boeing tribal lore).
Never flew the 707. The DC-8, by comparison, has one rudder and one YD. The YD can be deferred for dispatch with no speed or altitude limits.
The 727, on the other hand, was a dutch rolling animal. A YD on each of the two rudders cured the problem, but there were limitations if one was inop, and as I recall, no flight if both inop.
The gentle-giant 747 has one on each rudder, but only requires one for dispatch.
A company I worked for who had a survey Twin Otter added a YD to stabilize the platform for survey work. The aircraft would move around a bit in yaw while in turbulence and hurt the data. It didn't seem to have enough muscle to do the job and would eventually result in a skid. We usually turned it off, as they couldn't resolve the problem.
For the OP, I couldn't find a picture, but the one on the Twin Otter looked like a DG compass gyro. If that helps...