Thou didst divide the sea by thy strength. A clear reference to Exodus 14:21 (comp. Psalms 77:16; Psalms 78:13; Psalms 106:9). Thou brakest the heads of the dragons in the waters. The dragon (tannim) is frequently used as a symbol of Egyptian power (see Isaiah 51:9; Ezekiel 29:3; Ezekiel 32:2).
The allusion here is to the destruction of Pharaoh's host in the waters of the Red Sea (Exodus 14:27-30; Exodus 15:4).