In Thomas Wolfe's famous novel he writes,
...you can't go home again....You can't go back to your family, back home to your childhood, back home to romantic love, back home to a young man's dream of glory and of fame, back home to exile, to escape...back home to lyricism, to singing just for singing's sake, back home to athleticism, to one's youthful ideas....
Henry, like so many soldiers, especially those held as prisoners, cannot go back to what he was before the war; he cannot return to the carefree brother before going to Vietnam where he was made a prisoner of war despite the efforts of Lyman, his brother, who makes every effort to restore Henry to his former self.
Something died inside Henry; he had to shut it off while he was prisoner, and now he cannot turn it back on, even in his own home, or out in the country with Lyman where his emotions are as turbulent as the water he steps into, to cool off after his agitated attempts at frivolity. With the strong current and flooded waters of the river, Henry cannot control his direction, and he is swept away; detached from reality, he realizes he is drowning as he says in a detached voice: "My boots are filling." With his drowning, then, Lyman "drowns" the red convertible, a symbol of brotherhood. He wants no reminder of the tragedy.