Pearl Harbor: The Seeds and Fruits of Infamy - Ludwig von Mises ...

40 Pearl Harbor: The Seeds and Fruits of Infamy
Trade Treaty with Japan Ended
As the United States’s commercial treaty with Japan had
expired on January 26, 1940, Roosevelt was able, on July 5, 1941, to
prohibit the export, without a license, of aircraft engines and strategic
materials to Japan. Th en on July 31, he embargoed aviation
gas. From that time on, U.S.-Japanese relations deteriorated, as
artful diplomacy alternated with concerted acts of harassment.
Th e international situation, both in Europe and in the Far
East, was becoming increasingly ominous during the summer of
1940. Our ambassador to Japan, Joseph C. Grew, warned FDR
that an oil embargo might cause Japan to institute sanctions
against the United States, and that sanctions could lead to war. In
spite of his warning, however, we banned the export of aviation
gasoline to Japan. Japan resented this move. To compensate for
the loss, she began to build planes that could operate on ordinary
gasoline.
Japanese Diplomatic Code Broken
In August the U.S. Army and Navy communications experts
succeeded in breaking the top Japanese diplomatic code. Japanese
messages at that time were encoded on an extremely intricate
kind of typewriter, actually two typewriters connected by wires,
with complex coding wheels and switches. When a message was
typed on one machine, the words were printed out mechanically
on the other in code. Every few days the arrangement of coding
wheels and switches was altered so as to change the cipher. To
break this code it was necessary to build a machine that could do
what the Japanese machine could do and that would give the
same results as the Japanese machine would give whenever it was
adjusted. And this task had to be accomplished without having
any clues as to the nature of the encoding typewriter or of when
and how the switches and coding wheels were altered to change