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)).