I know this is a very oversimplified statement, but it seems to come a lot during World War 2 discussions.
Specifically, I'm interested in the "British intelligence". I know of the immensive loss Soviets faced, and the incredible rate of American weaponry and vehicle production that they Lend Leased.
When I think of British stereotypes during the Second World War, I think of Bletchley Park, spies, intelligence gathering, sabotage, and daring commandos.
How accurate is this?
It is actually fairly accurate. 1939, the US had 22,4% of the world GDP, in 1944 it was about 40%.
The Heer suffered 65% of their casualties on the Eastern Front (2 124 352 men). Total axis losses on the eastern front, dead, missing and prisoners were about 9 878 000 men.
The Soviets (and their allies, including the Polish 1. and 2. Army and a Romanian division raised from prisoners) lost about 12 331 000 men in dead, missing and prisoners (many of which were on purpose starved or worked to death in German prison camps). This is not counting the huge amount of dead Soviet civilians.
Considering that the total military death toll of ww2 was 22-30 000 000, the ~16 000 000 total military deaths (on the battlefield and in prison camps) on the eastern front accounts for about 53-73% of the total military deaths in ww2.
As for British intelligence, they did build on the Polish breaking of the engima, made extensive use of commandos, kept in contact with all resistance movements and much else. They did invent many of the best innovations of ww2 (while the US adapted them for mass production and churned them out in massive numbers). This is however much harder to quantify.
Personally, I'd say that British stubborness, fighting alone June 1940 to June 1941 was their largest contribution to ww2. That takes quite some determination and bravery!
Edit: 1941, not 1942.
I'd say "American steel & oil" would be more accurate. US production of both was absurdly higher than any other country - especially oil, where American production in any one year was triple that of every Axis country during the entire war.
To specify, all Axis powers combined, through every method, produced 67.0 million metric tons of oil from 1939 - 45. The US in 1942 alone produced 183.9 million metric tons, and that was the lowest year of American participation in the war. The Soviet Union produced 110 million metric tons from 1941-45, for another comparison.