What does John see when these four angels were released?
Revelation (Apocalypse) 9:16 (ESV)
16The number of mounted troops was twice ten thousand times ten thousand; I heard their number.
As the four angels were released, John sees mounted troops, soldiers on horseback. This indicates that these four angels had this cavalry of troops at their command.
16 The number of mounted troops was twice ten thousand times ten thousand; I heard their number.