Call Sign 7 is the name of the publisher, not the name of the game, which took me a while to figure out when visiting their site. The name of the game is Battle of Britain.

It’s a 3D 2-player war game about the air war on Britain by Germany. Each game requires you to fulfill a series of unique missions.

They’re giving away $1000 to whomever sends them a picture of a game in session in an “unusual place”.