In article , Brian Reay wrote:
some systems rotate the
gyros on a tourbillion like mechanism but these defeat one of the objects
of a 'strapdown' system).

Ah the good old "Carousel". That was the model of INS that had ovens for the
rate gyros that ran at 69 degrees F. I think Concorde may be the last
British Airways aircraft to use these, all the rest use IRS with laser
gyros.