Most military histories of the war in North Africa, and especially those produced from a British point-of-view, emphasise the greenness of the American troops which landed there in 1942. There is a tendency to compare them unfavourably with the battle-hardened Germans (and British) who'd already been fighting for three years. The Americans had a lot to learn in 1942 (though everyone agrees they did learn quickly).
Yet those same histories will also suggest one of the keys to the British finally defeating Rommel in Egypt and Libya in late 1942 was the arrival of large quantities of the excellent American Grant and Sherman tanks. British tanks like the Valentines and Mathildas used in the region between 1940 and 1942 don't seem to have been anything like as good.
So my question is, how was the United States able to produce such good designs and such well built tanks so early in the war (early from a US point of view)? Without experience of war and with an isolationist mentality up until 1941 where had these excellent tank designs sprung from? Why weren't their tank designs as green as their troops?