Definition of "unbrokenly"

After yet another check, there was once again a "Deltic" demonstration that no A4 would have been able to rival with a 340-ton load, speed being maintained unbrokenly at between 92 and 85 m.p.h. from Little Bytham up to Stoke Summit, where we were exactly 10min ahead of time.

1963 September, Cecil J. Allen, “Locomotive Running Past and Present”, in Modern Railways, page 187