In summary, most American marches use seemingly simple chord progressions for the sake of creating a melodically pleasing sound, however composers often complemented their marches with interesting chords and rapid chord changes—using chromatic harmonies, sevenths extensions, and secondary dominants. A detailed discussion of chord progressions follows. (Recommended reading in conjunction with these details: Chord progression and Scale degree.) Here is code for the chord progressions of the first strain of "Semper Fidelis" by John Philip Sousa. Note, each bar pair (e.g., |G7|), represents one of a total of 16 measures. |G7| |G7| |C| |C| |G7| |G7| |C| |C| |G7| |G7||C| |C|G7/B| |G| |G| |D7||G7| The first strain begins with a very simple V-I progression (see chord progression basics), creating a wave-like sense of tension and relief within the chord. The use of dominant seven chords makes the V chord stronger and is used in many marches. In the middle of the measure, before the trumpet "fanfare", the chord alters to C♯dim7 instead of remaining on C. This leads to a G7 chord (rather than to a D minor chord), and is an example of a common-tone diminished seventh chord. This chord leads into the V chord (G), then to a D7 chord. Here a D chord in the key of C would be the ii chord (as all ii chords must be minor). But the D chord here is not minor. Rather, it is known as a "secondary dominant", i.e., a dominant chord borrowed from different key. (A secondary dominant naturally leads into a chord other than the first (or I chord); here it leads into the V (G7)). Here is code for chord progressions of the second strain. |C| |F|G7| |C| |C| |G7| |G7| |C| |C|G7| |C| |F|E7| |Am| |A♭7| |C| |C| |G| |C| As with most second strains of march music, rapidly changing chords are featured: a legacy of Sousa. The IV chord is used here in marches to create an "uplifting" and lyrical sound which tends either to resolve back to the I chord—or to proceed into the V chord, as it does here. At the tenth measure, (|F|E7|), which restates the main theme, Sousa uses a "deceptive" chord change. Instead of using F to G7 to C (as in measures two and three), the chord goes from the IV (F) to V7/VI (i.e., E7), to the VI (Am). The main melodic theme uses the same notes,