Most of the Legionaries’ prayers are made up of the Rosary, but after that comes the Catena or chain, made up of the Magnificat with an Antiphon from the Song of Songs:
Who is she who cometh forth as the morning rising, fair as the moon, bright as the sun, terrible as an army set in battle array.
They conclude this part with the Collect from the Mass of Our Lady Mediatrix of All Graces.
So, for someone coming from a background of Sung Vespers, this is a prayer crying out to be sung!
* * Catena Legionis PDF : 4 A5 pages – print 2up for a booklet
And here is a quick recording of the antiphon to get you started reading the music.