All these 'how many yrs behind' argument is really an exercise in futility in my opinion and never lead to any productive discussions. First off it is very subjective and secondly technological advancement are bridge at different rates between each country and each area of expertise.
One can argue that 1935 the average layman will probably say that UK is years ahead of the US but within a span of a decade not only has the US matched the UK but surpassed them in terms of military advancement.
Thank you! Technological development is a highly non linear process.