Just one.
Or a lot of these:
The unit cost of a Lancaster was a little under £50,000. The unit cost of a B17 was about US$240,000. The GBP to USD rate was fixed at 1 to 4.03 from 1940 to 1949 which made the Lancaster unit cost about US$190,000.
The spreads for both the U.S. dollar and the...