On November 24, 1921, Whittlesey booked passage on the S.S. Toloa, a steamship owned by the United Fruit Co. bound for Havana. Prior to this, he had put his affairs in order and paid the rent to his landlady for the following month. On November 26th, after having stayed up late drinking and talking with other passengers, Whittlesey walked to the rail of the ship and jumped overboard. None of his friends or relatives had known about his travel plans and were thus disbelieving when the news arrived from the captain of the ship that Whittlesey had been lost at sea and that he had left behind letters to those close to him. The letters were addressed to his parents, his brother Elisha, his brother Melzar, his uncle Granville Whittlesey, and to his friends George McMurtry, J. Bayard Pruyn, Robert Forsyth Little and Herman Livingston, Jr. None of the letters revealed the reason for his suicide and the recipients refused to make them public. Several theories existed at the time as to what had pushed Whittlesey to such depths of depression. Those close to him believed that his death could be counted among the War casualties in as much as it was his sensitivity to the constant reminders of the destruction of the War that drove him to suicide. Some believed that his suicide was caused by feelings of guilt: the possibility that he had given incorrect coordinates to the 'Pocket', thereby causing friendly fire, or having refused to surrender to the Germans, leading to increased loss among his men. Others believed that it was his modesty and inability to adjust to the life of a hero that caused the depression that eventually ended his life. Whatever the exact reason may have been, it is clear that Whittlesey's death was indirectly related to the unhappiness which befell him after his experiences in the War.