The Siren is a retro style shooter where you shoot from your cannon at troops who are parachuting in.

It's a very simple shooter that might seem familiar to you old school gamers. The cannon will get hot requiring you to wait occasionally and the game gets progressively difficult.

The official blurb says:
War has struck your country.
Enemy forces are invading your lands.
Reload your flak and kill all paratroopers.