Prior to 1967 no female participants had officially completed the Boston Marathon.
Having signed her entry form K.V. Switzer, Kathrine's gender went unnoticed until the race was underway.
Jock Semple, the Race Director spotted Kathrine wearing an official race number, and took it upon himself to right this unprecedented wrong!
She tells Sean Moncrieff what happens next.
You can listen to the full interview here.