Why did Hirohito appoint Tojo as prime minister?

[1nt17cs152.ritvik]

@America at war! (1941– ) (Part 1)

In witness whereof, we have hereunto set Our hand and caused the Grand Seal of the Empire to be affixed at the Imperial Palace, Tokyo, this seventh day of the 12th month of the 15th year of Shōwa, corresponding to the 2,602nd year from the accession to the throne of Emperor Jimmu.

Did the Japanese use a different calendar as compared to the Gregorian calendar?