In one aeroplane type, the maximum landing gear extension speed was 300KIAS.
The aeroplane wasn't fitted with speed brakes and one day a pilot decided that lowering the landing gear at 300 KIAS would increase drag and allow a more rapid rate of descent.
They were doing slightly more than 300, so he raised the nose slightly, saw the speed reduce to less than 300, then lowered the landing gear.......
At Mach 3.2! This was in an SR-71. Fortunately it all held together and they landed safely after rather a noisy descent. From then on, the -1 was amended to include an IMN limit as well as an IAS limit.
Intentional gear down at M3.2 is still the record, although an X-15 had an uncommanded nosegear extension at over Mach 4!