Warhawk was first released in America back in August 28th, 2007, since then it has managed to sell over half a million times in that region!
To be exact, in the past week the PlayStation leaderboard statstics show the game has been played (online naturally) by 511,207 individual people (since launch) who purchased the game either online via a PlayStation Store download or at retail and played ranked matches. — Via N4G
Attendum: Due to a complaint I wanted to expand on these “sales numbers”. Since Sony never released official numbers, these are not the current accurate sales, but merely an indicator to show the game sold over 500,000 copies.