Commander David Cain is the leader of the World Army. He is the commanding officer of the US Pole Star, a sixth fleet aircraft carrier. He has been awarded the Legion of Merit and Bronze Star Medal.
Commander David Cain sails his boat toward Oblivion, Antartica, to wage war against the Old Ones. He was given the "all-clear" by Senator John Trelawny. He appoints himself as leader of the World Army. However he badly underestimates the enemy and does not seem to realize what this is not a conventional war. He believes they can easily attack the fortress with a military bombardment followed by a full-on assault.
Cain gives his speech to the 150 service men and resistance leaders who are invited into the tent for his speech against the Old Ones. He implements Operation First Strike, the day after Matthew Freeman and Lohan Shan-tung arrive at Antarctica. Matt tries to convince Cain that his plan won't work, telling him that lots of people will die without need.
Six Super Hornet planes fire infrared, homing surface-to-air missiles, supported by other cruise missiles and Sea Darts at the Old Ones' palace. Scarlett Adams raises a blizzard to cover the World Army's assault by ground.
Cain thinks he has damaged the Old One's fortress but it turns out that this is an illusion. When the World Army arrives, they now see the palace is intact. At the same time, the forces of the Old Ones came pouring out the gates. Cain realizes he has been tricked and watches the slaughter of his soldiers, horrified. When Matt causes a chasm, he is shocked. When one of his staff officers asks for further orders, Cain is resigned and walks back to his tent.
The dead was endless and the hospitals had been working around the clocks, and eventually ran out of equipment and bandages. Cain orders a mass evacuation as no one has the energy to fight, ammunition is low and death is everywhere.
A man called Omar, has come across the ice with the World Army as a prisoner. Cain is holding Scott's message to Matt in his hand. They all believe it is a trap, but Cain says that he has interrogate the prisoner. Lohan asks if he can have five minutes to torture Omar. Cain is undecisive when Matt asks for his opinion, but agrees with Richard. He admits that his plan was a disaster and that he has lost the right to advise you.
He is horrified when Matt and Richard Cole are captured. But he knows that they cannot do anything to help them. After realizing that he can do nothing more, he decides to return to America on the US Pole Star after evacuating the remainder of the World Army.
After the Old Ones are vanquished, he becomes the Vice President of the New United States even though he was completely useless, according to Holly.
Cain has bright blue eyes. His face is grave and composed, although Richard Cole notices that when Matt questions his Operation First Strike, there are two red spots of anger on his forehead.
Although Cain eventually admits that 'Operation First Strike' had been a mistake, he does not feel that he is at fault for the attack on the Old Ones' palace since he believes that anyone could have made that mistake. He also does not feel guilty about delivering the leader of the Gatekeepers straight into the enemy's hands.