If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Battle of Okinawa, April, 1945. Crouched behind the trigger of an anti-aircraft gun on the destroyer USS Callaghan you wait, scanning the sky. Black dots on the horizon, Japanese Zero fighter planes - lots of them. The time has come, It's Zero Hour, Can you do this?
Drag mouse on the screen to aim the gun. Press mouse button to fire.