Gets hard
I would have put it down a long time ago if not for the ability to advance ranks based on score. I made it to 2nd Lt and 30 minutes before karking it. Eventually get some slow-down as the screen fills, but it's all good.
The copters and planes prevent there being any sweet spots to just hang, and the weapon drops mean you have to get in the mix, as you don't survive long without a steady suppy of bombs.
Great game, I'll have to keep playing just to see where the rankings stop. Extra lives and some sort of total nuke pick-up would be good.