Commentary for Numbers 33:6

ויסעו מסוכות ....ויעברו בתוך הים המדברה, “they journeyed from Sukkot ....and they crossed through the sea till they came to the desert.” The spirit of escaping from slavery in Egypt prevailed until they had run out of water three days after emerging from the sea of reeds.

This is alluded to in Exodus 15,22 where they began a march toward an uncertain future in the desert of Shur, one of the deserts described elsewhere as ”this great and terrifying desert.” (Deuteronomy 8,15)