One of the earliest efforts of this type was in 1950's, by Hiller Aircraft - and you can see the helicopter itself in the Bay Area, in the Hiller Aircraft museu

One of the earliest efforts of this type was in 1950's, by Hiller Aircraft - and you can see the helicopter itself in the Bay Area, in the Hiller Aircraft museum. It achieved flight and was tested by US Navy & US Army. https://en.wikipedia.org/wiki/Hiller_YH-32_Hornet https://en.wikipedia.org/wiki/Hiller_YH-32_Hornet