Shofar History and Tradition
The shofar is mentioned in the Torah. An instruction manual, straight from the sources.
The following is the order of the blessings: One recites the Patriarchs, the Might of God, the Sanctity of the Name, including Kingship verses in it, and does not sound the shofar; the Sanctity of the Day and sounds the shofar, remembrance and sounds the shofar, shofarot and sounds the shofar... so taught Rabbi Yohanan ben Nuri. Rabbi Akiba said: If he does not sound the shofar with the saying of the kingship verses, why say them? Rather ... he includes the kingship verses with the sanctification of the day and sounds the shofar, remembrance and sounds the shofar, shofarot and sounds the shofar. (Talmud, Tractate Rosh Hashanah 4:5).
The reference here is to the main service of Rosh Hashanah, which was, in the rabbinic period, the morning (Shaharit) service. At some later time, this practice was changed, so that the sounding of the shofar and the reading of biblical verses connected with it were postponed until quite late in the day. The rabbis explained this postponement as follows:
It once happened that they sounded the shofar at the beginning [of the day]. The enemy [the Romans] assumed that this was the signal for an uprising against them so they attacked and killed them. (PT Rosh Hashanah 4:8 59c)
Although the historicity of this specific event is not verifiable, what is clear is that the shofar, like the trumpet of the Romans, was an instrument used in biblical times to signal battle, as exemplified in the story of Joshua and the walls of Jericho. Sounding it later, to avoid any misunderstanding, when it was obviously a part of the ritual of the day, was therefore plausible and indeed advisable.
Yet, moving the sounding of the shofar from Shaharit [the morning service] to Musaf [the additional service] was not completely appropriate. Indeed, the talmudic rabbis found it problematic that the main mitzvah of the day was not performed until such a late time. An additional blowing of the shofar was therefore added at the conclusion of the Torah service (without the biblical verses that once accompanied the act), and the sounding of the shofar was never returned to its original place. Interestingly enough, then, what has come to be seen today as the main shofar service was originally a secondary service.